For Tel Var farming, it seems like the optimal number of people in a group to farm is 3.
1 to 2 DPS. Tel Var farming means turning all districts and doing the bosses. Everything else is inefficient. I've seen people soloing bosses in 1 1/2 minutes using a full DPS rotation. My own speed is more in the 3 to 5 minute range with my PvP build. At my speed, if you play with more than a duo, you'll go through the bosses faster than the respawn rate. Anything more than two people is fine for fun, but a waste of time, if you're strictly after Tel Var. Play in Shor. Take advantage when others have taken most of the flags. Isolate bosses into areas where other players tread rarely, but don't be a *** when they do show up. Play in a CP campaign. In no CP bosses are more dangerous and tedious, although you may have less competition from players.
There are a couple of ways to go. If you are used to high-end PvE, a full DPS rotation will mow down bosses, and particularly their adds, so fast you minimise risk that way. If you're more like me, you play a balanced PvP / duelling build. An infused weapon with a prismatic enchant will work wonders for your DPS, while simply weaving your spammable. The tankier you are, the more of an advantage you have around bosses over gankers trying to attack you, particularly stamblades. Do focus the PvPers, if they attack, but play conservatively and let the boss AOE kill them, if possible.
If you play a nightblade, you always have the option to cloak away from PvP, and also shake aggro from bosses, if you wish. Imperial Physique and a tanky set, like Fortified Brass, can help make boss fights comfortable, while retaining light armor and good damage. Ranged builds are easier than melee builds, unless you take measures to minimise ground AOE, such as Leki's and Blade Cloak. Bahraha's does not work for the AOE in IC, as far as I know. You can choose to kite and ignore adds. On the other hand, one well placed Dawnbreaker is almost good enough to mow down a wave of adds on it's own. My preferred and comfortable alternative, as a magblade, is resto ult and AOE (Sap Essence) for adds. Be sure to have retreat sigils on you to bank every so often. On PC, get Miat's addon, which will tell you the status of the flags at all times, without having to go to the map.
Tips for specific bosses:
Take the Memorial Flesh Atro boss to the Imperial Prison entrance, and an add often gets stuck in the walls, there, which prevents further waves of adds.
For the Memorial Ice Atro, Forward Momentum helps your mobility. If you heal from your damage (Bloodthirst, Funnel, Puncturing Sweep), attacking into the boss while having up Vigor, or the like, when he spews out his ice AOE, can be the most efficient solution, but you'll have to test your build to see whether your healing is strong enough.
The most dangerous attack of the Flesh Atro arena boss are the AOE poison pools. These are targeted at you, even cloaked nightblades that are in the fight. Don't run. Move around at a normal pace and be conscious about the area YOU are effectively covering with the pools. Move just enough to stay out of the pools. The slower you move, the less area you cover, and the more room you leave yourself. This fight is less messy to solo than it is with more players.
When the Arena Daedroth boss attacks you with a fireball, let yourself be knocked back, but immediately break free, so you land on your feet. Make sure to have space behind you. The way you typically die to this boss is, if there is no space behind you and you land in the AOE. The boss is also prone to charge you right after. If you are in a confined area and he prepares a fireball, run towards him, so you have room to be knocked back.
Avoid the Arboretum Harvester boss, if you are solo. At 50% health, she will stun you, and you have to break free and kill her feasts, which you have to individually target, otherwise she heals back to full. If you are ranged, and you have the damage, you may succeed, but this boss tends to be more hassle to solo than it's worth. It also puts a snare on you that cannot be cleared with Forward Momentum.
Not much to say about the Arboretum spider boss. Quite easy, if you ask me.
The Ogrim in Temple is straightforward. Avoid / roll out of his ground AOE when there is an expanding red circle around him, as it hits strongly and knocks you down otherwise. At around 50 to 45% of his health, he will thump his chest and you have to interrupt him, so he doesn't heal back up. He may do this a second time before the end of the fight.
The Temple lich boss can be hard to deal with, if you are melee. This is where Leki and Blade Cloak really helps. As a ranged build there's just a lot of kiting and running. Watch your stamina. You can AOE the adds or ignore them.
For the Nobles Twilight boss be sure to focus and destroy the portals immediately when he creates them.
The Nobles Bone Atro boss drops big puddles that inhibit magicka and ultimate use, so keep an eye on your stamina, and roll out of them.
For the Elven Gardens Clannfear boss, be sure to watch your stamina and health. Keep your health up and, as a light armor build, keep your shields up. When he tries to eat you, break free immediately. Reserve your ulti for when he spawns adds. I find the main thing about this fight is watching your resources. If someone wants to gank you, they will do it when the boss tries to eat you.
The Elven Gardens Eye boss is easy with the right strategy. He will spray strong lightning AOE onto the ground. This must be avoided. Always reposition and make sure you never have some of his AOE behind you, otherwise he will knock you into it. If you cannot get close enough for attack, simply wait. Let the fight come to you. I prefer clearing the Legion Zero soldiers up and down the strip, before the fight, then let him chase me up and down. As a ranged player it is easy to stay out of the AOE. As a melee player, when he sprays out the AOE, roll through him, so you end up on his opposite side.