If you don't feel like watching 16 minute video per dungeon to know the specific mechanics for every boss, here's a comprehensive list for you. (Though I'd still advise watching some videos or learning by doing since some mechanics are pretty tough to explain). Said list assumes that the group is decent. Not good, but not abysmally bad either. Meaning the tank has proper resistant tanky gear and blocks and bashes, the DPS pull 10k+ dps (you can complete these dungeons with 10k+ but obviously, you ought to aim higher), and the healer heals with healing springs and is reactive enough with flash heals/healing wards.

At any rate, here's to hoping you won't go into dungeons being completely clueless. I'll focus on boss mechanics since the trashwaves are pretty standard - aoe DPS and try not to stand in red circles.

ALDMERI DOMINION DUNGEONS:

Auridon - Banished cells I : Epic quest to banish an evil lich king. Said lich king ports around the room and every 12-15 seconds summons a lot of fire aoe around the room, which you have to get out of asap. At the same time, he will spawn a blue ball in the middle-east of the room (at his initial spawn point). Said ball will move towards him and, as DD, you need to kill it asap, before it reaches the boss. Otherwise it will heal him and make your efforts in DPSing him worthless. Every 12-15 seconds, the boss will ignore the tank's taunt, turn around, and throw a skull projectile on the player furthest away from him. Said projectile stuns for 2 seconds and one shots most squishy builds, so make sure to stay alert and block/dodge/shield through it.


Grathwood - Elden Hollow I : Racist High Elves and their Orc slaves chill underneath the AD capital.
Last boss is called Canonreeve whatever. She is a stationary boss that, as usual should be tanked facing away from the group. She does a huuuge AOE attack which everyone, including the tank has to get out of, otherwise it's a one shot. Also, she will periodically turn away from the tank and cast a small circle underneath a player's feet. Said circle will suck and stun the player in, but you have more than enough time to get out of it. Healer should be ready with a flasheal just in case.


Greenshade - City of Ash I : Formerly rich Bosmer city that got sold by said Bosmers and subsequently ruined by daedras. (Cf: Deal with the Devil)
Last boss is a daedric archer that will port around the room and spawn flame atronachs. He does no damage, the atronachs do no damage, and the fight is boring. However, one of the bosses called Razormaster something (2nd boss found on the east side of the dungeon, top of the stairs) will be a NB boss fought on a very small platform. Said boss will throw fire bombs all around the platform, and while you can stand for one tick in the fire, make sure you move and react fast, and get out. Same goes for the Flame Atronach boss found right behind the barricade in the middle of the dungeon.
It's a fire-fire lava-lava dungeon, so double emphasis goes on dodging the hell out if you're a vampire.

Malabal Tor - Tempest Island: Maomer (Sea Elves that look like blind vampires) prepare to invade AD land and you decide to meddle.
Among bosses with notable mechanics, there is Stormfist, a giant-ass storm atronach that will "bump" players. Meaning that periodically, he will do an AOE circle around him, and while it won't one shot, the players will be thrown in the air. I usually stay in it on purpose just for fun.
The last boss is the Chief Maoemer, can't remember the name but it hardly matters. So, she does a ground huge AOE attack that will one shot even most tanks. Seriously, I had 30k shields with heavy armor + ebon + maxed resistances on my mana sorc tank and it brought me to 10% health. Safe to assume that it one-shots even the tank. So everyone needs to get out of this huge circle. Apart from that, she will teleport onto a random player. This teleport one shots, but you see her coming. Well more like gliding (just imagine Voldemort/Dementors gliding above ground, only not in slow-motion) so you need to block it or dodge. Preferrably dodge.

Reaper's March - Selene's Web : Mages' guild expedition to capture Selene, the queen of feral bosmer in order to torture and poke and prod her soul for eternity.
The archer boss on the left (West) side of the dungeon has 3 spectral panthers fighting for him. While it is crucial that the tank taunts them since their attacks kill most DDs and Healers, you only need to DPS the boss. He will roll dodge a lot around the clearing, but he's pretty easy to get down. If you focus the panthers, they will keep respawning. So, focus the boss.
The cute giant bear boss in the right (East) side of the dungeon will do charge attacks that you can easily side step. He will also have a lot of strangler adds. Don't focus them, they will die once the boss is down. Focus the boss.
Last boss: Selene has 3 phases. First, you are standing on a web and she's in spider form. Don't waste your ultis for this phase is pointless. Just bring her to 50%, at which point, she will make the web crack and you will fall all together in the room underneath, her still in spider form. Keep up the DPS and keep your ultis. Around 10-15%, she will pull you into unbreakable cocoons to her, and transform into a Bosmer chick. Her Health Bar will replenish to 5M / 100%. And that's where the real boss fight begins. So, Selene will do a heavy attack that will spawn a spectral bear on the tank. The bear will one shot, no matter what, but has a small radius of melee damage, so the tank as well as everyone in its way needs to get the hell away. The bear will spawn a lot, but once you get a grip on its rotation, it's easy to avoid. Additionally, she will spawn adds, more numerous as the time passes. Archers, Healers and Melee 2h wrecking blow spamming Bosmer. The tank will most likely not get the aggro of every add. Or if he will, he might forget about dodging the bear and die. Just ignore these adds and focus the boss. If you feel like your group has a low DPS output, then pack the adds with the boss (tank has to chain pull or use the Swarm Mother set for the distance adds), and AOE them down.


DAGGERFALL COVENANT DUNGEONS

Glenumbra - Spindleclutch I : Fighter's Guild expedition was hired to clean the cave and proved to be hacks. Now you have to save what remains of them and hear a giant-ass spider whisper you sweet nothings in a menacing yet oddly sexual manner.
So, spiders as well as spider bosses should be bashed when they start to eat out the corpses of their spider friends and heal. Otherwise, the dungeon is quick and easy, just like some people I know.
Apart from the last boss : the Whisperer. She has two attacks which won't go on the tank. One is called Arachnophobia aka Fear. It hits at random, and if it hits you, your screen will go white and you will be stuck in an unbreakable stun for 2 seconds. The other attack is called Spit. It is crucial that the tank faces AWAY from the group, because this spit is very difficult to dodge and one shots. So, best if the tank tanks her while standing on the small stairs behind the boss. As soon as the boss turns away from the tank, you have to dodge, because she will spit/arachnophobia you. The 2 DD and Healer should not be packed but stand at equivalent distances from one another, so that you see the person on which she plans spitting. It avoids wasting stamina and DPS dodging for nothing. You especially as a mana sorc. Apart from that, she will periodically pull players to her in a cocoon and do a large AOE attack. Break the cocoon and get the hell out of it. At any rate, this fight is difficult for mana builds because of stamina regen issues. I know that I failed survivor's challenge the first time on HM since I had no stamina left to dodge the 3rd or 4th spit on my mana sorc. (And got so much crap for it, even though we got the achievement like 15 minutes later).

Stormhaven - Wayrest Sewers I : Breton traitors conspire against King Emeric in sewers of all places (idk why people keep thinking that sewers, cathedrals, basements and dark, shady places make for awesome plotting rendez-vous areas. If I were them, I'd do it in a nicely lit and totally not shady looking mansion or something, because nobody looks for evil cults in taverns and boudoirs).
At any rate, all bosses are fairly standard. The second boss in the room with the altars will port around and summon spectres. Said spectres do frost lines on the ground that will immobilize you but otherwise not do significant damage. They remain after the boss dies, so feel free to kill them before doing in the boss, but it's not mandatory.
The last boss will do a cone cleave attack that you can easily side step and tank can block. Periodically, she will disappear from the room and summon spectral bats. Just kill them with aoe damage, and if your healer's fast enough, you can even get a free repentance out of it.

Rivenspire - Crypt of Hearts I : Supposedly cheating woman got her soul shattered, imprisoned and tortured by a jealous husband under daedric infulence for whom "an eye for an eye" was simply not enough.
The Bone Colossus boss will keep moving around the room, so your ground dots will be mostly useless. Also, this boss is crosseyed, meaning there's a chance his charge animation will point one way, but he will go another. So be prepared for it, just in case.
Last boss: Twin Daedras Ilambris- Blue and Red. The Blue one is a melee 2h dude whose heavy attacks the tank must always block. The Red one is a stationary fire mage that will remain in the middle of the room. Best if the tank packs the Blue one on him so that you can dot him down. For this fight, once one of the Twins dies, the other will go into "enrage" mode. Meaning constant huge aoe damage attacks. Best if you kill the Red one first, if only because he does aoe stuns and fire lines on the ground around the room. While you can avoid the fire lines by side stepping them, they're annoying and hurt a lot, and the stun covers almost all the room, so there's that. Once the Red Twin is down, focus the remaining Blue one. His enrage mode consists of lightning small AOE bubbles on the ground and lightning strikes which are accompanied by dramatically raising his hands in the air. You can avoid them, and if needed, the tank can move the boss around the room.

Alik'r Desert - Volenfell : You help treasure hunters reach some fabled Dwemer treasure, killing evil Imperial treasure hunters along the way.
Quintus Verres : Untauntable boss. Yeah, he ignores the taunt, and as such will just aggro on a player. Hopefully said player feels tanky and is ready to block his attacks, cause they one shot. In the meantime, the tank can chill, go through his friendslist and think about his life. At 10% health, he will go back to his backpack, and summon a huge gargoyle. Said gargoyle will finish him and start the next boss fight. It will do a cone aoe attack that will petrify players, so best if the tank turns it away from the group. Otherwise, fairly standard.
Boilbite : Assassin Beetle boss + 2 adds. It ambushes on a random player and does small poison AOE ground dots, which you can escape.
Dwemer Steam Sphere boss : reached after a tunnel of steam. Said steam one shots, so you need to cross the tunnel at intervals when it doesn't fire. Otherwise, the boss does small aoe attacks which can be sidestepped.
Last Boss: 3 dwemer centurions - Blue, Red, Green. The Green one heals, the Red one will aggro on random players and do fire dots, and the Blue one will stay on the tank and do lightning attacks. Focus the green one first, if you can since it heals. Then red, then blue. The poor guy who has the aggro of the Red centurion has to move. Even with Hardened Ward on a sorc dps, you take too much damage to stay in one spot.

Bangkorai - Blackheart Haven : Crew of skeleton pirates straight out of Pirates of the Caribbean goes on a mutiny and needs your help with killing their captain. Said Haven also contains harpies and daedras because why not.
First Mate whatever boss: surrounded by harpies, she will charge a cast attack that does "void" on a random player and one shots him. The tank has to BASH it. You can see her charge her cast like a templar charges a dark flare. If you or your tank doesn't bash it, someone will die, and you'll have their death on your conscience, and it will all be very sad.
The Roost Mother harpy boss: teleports around the room and does a lot of fire aoe, so dodge, dodge, and again dodge.
Captain Blackheart: last boss. Emerges from the water in a really epic way. He will summon skeleton archers which the tank has to taunt and pull to the boss to kill them with ground dots, and will charge a random player and transform them into a skeleton for 15 seconds. Once a skeleton, you're useless. You cannot heal nor do damage to the boss, so feel free to run around and dodge the arrows from archers the tank hasn't taunted. If you're lucky, the boss will spare your healer. If the tank's the one being transformed, just block the boss' attacks (they don't one shot. Well unless you don't block/dodge) until your tank is back to normal.


EBONHEART PACT DUNGEONS

Stonefalls - Fungal Grotto I : Probably evil cultists need your help in cleaning a grotto perfect for their probably evil rituals. Said grotto has an epic goblin vs. dreugh fight for territory. You side with the goblins after killing their chief in an Xv1, if only because they look more sentient.
Second Boss: Goblin Chief King whatever. Will do the inner rage synergy on a player. Said attack explodes after 3 seconds doing aoe damage, so the player targeted by it should move just a bit away from the group before it explodes to avoid hurting others. (It's not a strong attack though, so feel free to stay packed if you feel like it). Additionally, he will cast a purple link between two players. As long as this link holds, both players will lose health and ultimately die. As soon as you see this link, the players bound have to move AWAY from each other until it breaks.
Dreugh King: last boss. Does a huge AOE attack that will one shot, so move out. He will also spawn 2 waves of mudcrabs that easily die from ground dots on the boss. Otherwise, fairly standard melee enemy. At 40% he will move to the right corner of the room and resume the same mechanics.

Deeshan - Darkshade Caverns I : Shady Dunmer hires you to clean his mine, turns out to be evil, and so you hunt him down through dwemer ruins lying beyond to avenge all the innocents you've killed while helping him.
Last Boss: Dwemer Centurion. He will randomly target a player and charge him with a red cone aoe in front of him. Said player needs to run. Don't stay in the red cone of death, just kite the boss around the room. The rest of the team can distance damage him. Otherwise, it's a fairly standard melee boss. Tank him away, DDs dps from sides/behind, healer heals.

Shadowfen - Arx Corinium : Abandoned Imperial fort has Nereids vs/ Lamias fight for territory. You help the Nereids, probably because they look cuter and have boobs.
Wamasu Boss: emerges like a badass from a waterfall and does lightning AOE. Said AOE touches all the water surfaces, so move on the land when it hits. Makes sense since water conducts electricity. (Well not water per se but the minerals contained within, but whatever).
One of many Lamia bosses (the one in the room with the lever you have to pull to get the drawbridge down) : will emit a shrill (a song maybe. at any rate, sounds like a shrill). During this channel, you will have to go under a protective purple sphere that will appear in the room. Said sphere will be located above the Lamia's pet snake, so don't kill it before the boss.
Last boss: Sellistrix, queen of the Lamias. The room will be mostly water surfaces with small patches of land. The boss will do a shrill aoe cone attack on the tank, so he has to tank it away from the group to avoid collateral damage. She will also summon lightning to touch all water areas, so when it hits, go on the land. When the lightning aoe goes on the land, move to the water.

Eastmarch - Direfrost Keep : 3-D projection of a dead Nord guides you through his ancestral home, which has been overtaken by an evil frost witch.
The boss in the very left side of the dungeon, where you have to stand on pressure plates to open the gate to it, will summon scamps who will one shot someone once they explode. When scamps appear - focus them, they die super easily.
The last boss: Frost Witch whatever. She will mostly ignore the taunt. Seriously, it says she's taunted, but she will keep damaging other players. She has several mechanics: 1. She will do a drain animation on a player. You have to CC break instantly. As long as the drain holds, she heals. For a lot... 2. She will teleport to a player and launch an aoe attack, which one shots. Everyone needs to get out of it. 3. She will summon several frost atronachs during the battle. Said atronachs die easily from the ground dots, no need to bother with them.

The Rift - Blessed Crucible : Dunmer gambler asks you to fight in gladiator style battles, which he rigs in your favor (which is mostly pointless since you would've won anyways). Consequently, the public as well as arena competitors turn on you, and you have to fight your way through them to save the unfortunate gambler.
The Pack : Standard waves of adds followed by 3 bosses which turn into werewolves at around 30% health. Just bash the healer boss, and otherwise DPS.
Second-to-last boss : dunmer dude with 2 flame atronachs around him. Kill the atronachs - they heal the boss.
Last Boss - Lava Queen, whom you fight on a platform surrounded by lava. While seemingly a standard melee boss, she will periodically do fire lines all around her. These fire lines are very difficult to avoid if you're in melee, and will one shot. Stay ranged. You can clearly see the animation before she launches the attacks (she crouches a bit on herself and starts casting), so just get the hell away from the boss. The tank should too. These lines really hurt Additionally, she will summon flame atronachs that will grant her temporary invincibility via channels from them to her. They will be around the edges of the platform in the lava. You need to kill them, then resume DPSing the boss. But seriously, avoid the fire lines, they're a b***.

Coldharbour - Vaults of Madness : Free the ghosts of imprisoned workers of the Mad Architect in a dungeon with lots of potential for fall damage. Set workers looooove to talk, meaning the quest takes ages. Just like the Blessed Crucible and City of Ash, it's a fire-fire lava-lava dungeon, so vampires beware.
First boss : Specter. He will do a channel on a player. While the channel holds, ALL the damage you do to the boss will be transfered to the player caught. So, if you really want the no-death run, just stop all DPS when it happens. And avoid dots. Otherwise, make sure the player's sacrifice was for the greater good and avenge him.
Second Boss: Harvester. She will stun a random person for 20 seconds. 20 seconds of unbreakable stun is annoying but there's nothing you can do about it, so just chill. She will also have healing bubbles going towards her from all sides, just like any standard harvester. Said bubbles are down in one or two Force Pulse, just make sure you don't forget them.
Grothdarr : Does really cool lava aoe, but make sure you side step.
Titan boss : does a jump-stun and randomly aggros on a random player with a wide line of fire reaching all across the room. Just dodge it.
Last boss - Mad architect aka the Boss with by far the coolest mechanics in-game. It's a stationary lich boss that will summon daedra casters and melee zombies from around the room. These will die from ground dots, just make sure the tank pulls them to the boss. Then, he has two mechanics: if he summons a purple globe around him, stay close to him for the duration. Going outside will one shot. If however, the ground beneath his feet glows purple, gtfo dodge. Staying close will one shot.


And that covers pretty much every "normal" dungeon. Bear in mind that in normal mode, the mechanics are unlikely to one-shot, and bosses won't have as much health. Compare 5M+ in the vet hard mode of these dungeons to 1.9M in normal mode. However, I still would suggest obeying the whole "AOE - one shots" mindset. I mean, if you get used to standing in the red because normal modes can be done while being naked, then you will do so once you move on to veteran versions of the same dungeons, which are far less forgiving.