Pull until you either can't or don't want to using aggro moves, throw in a cooldown every now and again, let the DPS single targetting in a mass pull eat dirt and continue.

Then realize you're playing DRK and in a dungeon where you don't have Abyssal Drain and die a little inside because you're only worthwhile AOE is on a sixty second cooldown.

Pop off on the boss with some enmity combos, swap to DPS stance, cooldown accordingly and wail on the boss until it dies. Go back to tank stance and repeat until the dungeon is over.

Eight man content in roulettes, you're basically a DPS who might have to pick up an add or something. Toss a voke shirk on whoever's MT to give them more enmity and put yourself ina good position to grab the boss if they die and basically treat it like a dungeon boss. Alliance raids are basically the same except you can't voke shirk, so if the MT dies there be ready to grab the boss.