Trials: 5pc Tava's Favor, 5pc Footman (flex), 2pc Blood Spawn
Dungeons: 5pc Bahraha's Curse, 5pc Footman (flex), 2pc Blood Spawn (flex)
Flex Options: #1 Alkosh, #2 Ebon (for trials tanking) or any set that supplements damage/healing (for dungeon tanking) like Twice-Born Star, Julianos, etc.

Each of these sets is viable in both dungeons and trials. For example, as the off-tank in Sanctum against the Mantikora, a NB tank using 5pc Footman and 5pc Bahraha's Curse can easily self-heal the Serpent Image during the Black Hole Phase, meaning you can send 3 dps instead of 2 dps and healer, which speeds up the phase and results in an overall shorter fight.

The general strategy is to go all-in on magicka. This is contingent upon a number of factors, namely your health pool, but is viable as both a starting point (as you figure out your own preferences for tanking and your setup) and a potential endgame final allocation.

Assuming you have proper mitigation values, which I'll get in to later, your maximum health can be as low as ~26k comfortably, even in vMoL and vSO. Allotting all of your points into magicka is okay, since you can use Health and Prismatic glyphs to supplement your health pool.

My allocation is slightly different than any other magblade I've spoken to to-date, but it's not that much different. I've fused the meta allocation for magblade dps and the allocation for general magicka tanking into a hybrid allocation, which I use to maintain a single character capable of actively switching builds entirely on a whim. This affords me the ability to be a strong main tank, a 30k dps, a healer (or off-healer or 50/50 split) for any trial.

This allocation is a general guideline. There is room for flexibility on just about every star you invest in. Depending on your focus (full tank, tank/dps hybrid, etc.), you will redistribute these points to boost the stats you deem appropriate in the context of your content and role preference.

The Mage
10 pts. Blessed
12 pts. Elfborn
70 pts. Elemental Expert
75 pts. Thaumaturge

The Thief
70 pts. Magician
50 pts. Warlord
30 pts. Shadow Ward
17 pts. between Mooncalf and Arcanist, with stronger emphasis on Arcanist (if not all 17 pts.)

The Warrior
80 pts. Hardy
36 pts. Elemental Defender
36 pts. Thick Skinned
15 pts. Quick Recovery

Again, this allocation will vary depending on a couple of factors, with race being the primary influence. For example, as a Breton, I allocate fewer points into Elemental Defender than most tanks do, which I redistribute into Hardy primarily. You may also want to consider spending your "extra" points on something like Expert Defender.

Surprise! This one is totally up to you. I don't even use a Mundus for tanking. Months ago I set out to determine what the best Mundus option for a hybrid build such as mine would be. When all was said and done, I determined that Mundus selection is not pertinent to tanking, so I always use the Thief for my dps setup. It technically benefits tanking to some extent, since crits on skills like Swallow Soul will afford you a crit heal as well. You can do literally whatever you want, and still be a super tank. If you want to supplement your damage, try going for something like Mage or Apprentice, or use Atronach for sustain.

Trials Tanking
Bar 1: Pierce Armor, Stalwart Guard, Defensive Stance, Swallow Soul, Siphoning Attacks. Ult: Aggressive War Horn.
Bar 2: Inner Fire, Stalwart Guard, Sap Essence, Swallow Soul, Double Take. Ult: Soul Harvest

Dungeon Tanking
Guard isn't necessary in dungeons, and it isn't necessary if all of your dps is melee and using Trap Beast.
Bar 1: Pierce Armor, Double Take, Defensive Stance, Swallow Soul, Siphoning Attacks. Ult: Aggressive War Horn (flex)
Bar 2: Inner Fire, Sap Essence, Deep Slash, Swallow Soul, Siphoning Attacks (flex). Ult: Soul Harvest

For trials tanking, you want to have guard active on any of your dps who are going to stay close enough to not break the tether. As mentioned above, it's more or less pointless to guard a stam dps running Trap Beast; However, the main exception is for your melee dps who are expected to eat damage being dealt instead of move out of the way. A prime example of this is on the troll boss in SO. Outside of these exceptions, you should be guarding your close-range magicka dps (like magicka DKs). In some very unique scenarios, you may want to also guard the main tank (such as the Mantikora's enrage/burn phase on vet, if you need to get rezzes and don't want your main tank to die to enraged DoTs and Cleaves).

For dungeon tanking, I say not to even bother with Guard at all. It comes in handy in some scenarios, particularly in the more difficult vet dungeons (vIP and vWGT), but for the most part, you don't need it. You always have the option of running it to boost the dps of someone in your party who may be underleved or undergeared, but aside from that, there aren't too many good reasons to take up two valuable skill slots with it.

Glyphs & Poisons
The first thing you should do when glyphing your gear is account for reaching your minimum health threshold. Everything beyond what you need to have a comfortable level of health (to avoid dying to "big hits" or "1-shots") should generally go into magicka, which will boost not only your sustain, but your self-healing and damage contribution as well. I put Prismatic glyphs on all three major pieces of armor (head, chest, legs) and magicka glyphs on all minor pieces (shoulder, gloves, belt, boots).

Jewelry glyphs are pretty flexible. Personally, I haven't had an issue with sustain since before IC was released, so I put spell damage glyphs on all of my jewelry for additional self-healing via Swallow Soul and Sap Essence. Other strong contenders are Glyphs of Shielding (reduced block and bash cost) and Glyphs of Magicka Recovery.

Weapon glyphs are really not that relevant for dungeons, so you can do pretty much whatever you want here. For trials, and perhaps some dungeon bosses, I strongly recommend running Glyph of Crushing on your off-bar and Vulnerability Poisons on your main bar. Your group will appreciate it, especially if you trade Footman for Alkosh.

Potions
About 99% of the time I use welfare potions (the junk you pick up just running dungeons and buy from vendors). There are some really good potions out there that you can use, but personally I find them to be an unnecessary gold sink. At the very least, make sure what you use is being supplemented by having Alchemy passives.

Traits
Some argument can be made for Sturdy on at least 1 or 2 pieces of gear. I don't use any Sturdy traits, and I don't use any Shielding glyphs. I'm not stating this as a means to brag; the point here is that NBs are built for sustain. With the right passives, CP, and skills slotted, you don't need to sink that much into additional reduced block cost. Do so if you wish, and if you're comfortable with it. But don't accept the mentality that it's absolutely necessary, or you'll be out of resources. That's simply not true for an experienced NB tank. As you gain more experience and are more comfortable with your weaving (see below), you'll find that you have a lot of leeway with your traits.

That being said, I recommend putting Sturdy on minor pieces, if you choose to do so. Infused traits belong on all of your major pieces (especially those with Prismatic glyphs). Every other minor piece is a discretionary flex trait.

There are a few buffs that you need to always keep active:
Double Take (Major Evasion), Crushing (reduced armor on target), Minor Vulnerability (for trials mainly, but as often as possible, given the internal cooldown), and Siphoning Attacks. Managing the up-time on all of these buffs is one of the more complex aspects of NB tanking. It's not so difficult once you get the hang of it, and some of these are common practice for other tanks as well, so if you come from a different tank to a NB tank, it'll be an easier transition for you with that experience.

In addition to these "mandatory" tanking buffs, you also want to keep Major Sorcery and Major Brutality active as much as possible, which you very easily get just by throwing a Sap Essence into you rotation from time to time. And yes, it is a good thing to Sap against a single boss for the buffs - the 20s of extra self-heals pays off in many encounters, especially if you have foregone a healer on your run.

- Sap Essence serves as an initial AoE taunt. It will almost always pull everything it touches to you immediately after you cast it. It won't hold their attention for long, but it lasts just long enough to sneak in a handful of Pierces Armors and Inner Fires without them running away. This is a strong opener, not just for the initial aggro component, but also because it allows you to start the fight with Sorcery and Brutality.

- This is the most important thing to learn and master as a NB tank: Light Attacks are your main source of sustain. The common misconception here is that saptanks rely almost solely on the procs from Siphoning Attacks to retain/regain resources - but this is not true. The proc% on Siphoning Attacks is a supplementary mechanic, not the primary mechanic. As such, you should be weaving a light attack in between everything. Yes, everything. Between buffs, between taunts, between everything, period. People ask me how I manage to perma-sustain without ever taking a shards, combustion, without sturdy traits or reduced cost glyphs,etc. - this is the reason why. It's because I almost never miss a light attack weave.

The trick (and this takes a lot of practice) is never missing a light attack weave without getting hit between block. Timing is key, and the sooner you get this mechanic down on an instinctive level, the sooner your will excel as a saptank. With Crushing and Vulnerability, the importance of doing this is further capitalized upon. Practice makes perfect (and I'm still not )!

- Without chains, it is crucial for you to stack melee on top of ranged. When you start a pull, find where the ranged adds are standing. Pick a spot where the most ranged adds are grouped together, and take everything else to that spot. The earlier in the pull you do this, the smoother the pull will go.

- Bahrah's Curse procs more reliably from Deep Slash, and so does Siphoning Attacks. Anytime you are not using Guard, I strongly recommend utilizing Deep Slash (not Heroic, that's for other classes).

- Know your group make-up. This one is more of a general tanking tip than for NB tanking specifically, but it's very important. Always know where your melee is at, and where they need to be (this includes knowing if they are running flanking and need the boss to be perfectly positioned to benefit from their set). The same applies to your healer and magicka dps, but they have a stronger ability to take care of themselves than melee builds do. Take care of your melee (don't forget your magicka dks)!