A few silly tricks I've learned that help Sin tanking. Hopefully this helps:
- Whenever possible (and viable), use force pull as a starter (but not at max range) even on boss fights where they don't move. It's free threat that you can't use often on the same mob. Also use it creatively on those tough elites.. Ex: knock one back and while they are in mid air backup slightly and very quickly pull them back. Again, free threat. Also as a "this coffee is hot don't spill it on your lap" disclaimer try to not pull something in then aoe it while it's buddies are out of range.. Not good times...
- Save your single taunt for a little bit into the fight and using it quasi-often on things like raid bosses that don't dump aggro. Understanding that people get aggro on different % helps.. Like dps getting aggro at 125%, healers at 110% or whatever the actual numbers are in this game.. A taunt to my understanding brings you to the top but only "just so".. having a mob forced to attack you right off the bat is cool and all, but it'll do nothing for you once the dps starts to unload. Also on big boss fights you may be losing ground but you may not know it right away due to the massive hp %.. Bottom line, taunts occasionally = good.
- No brainer stuff: Like other people mentioned here before, use your aoes on every cooldown, keep your def buff up (but not a priority before aggro), and if you are having energy issues with getting things off instantly use more free attacks in your rotations.
- Throw your bubble on someone you can stay close to without killing. I usually guard top dps since it just helps.. But make sure regardless you're in range of them to take their aggro without putting them in danger of aoes or swipes. So if you have to guard a melee guy instead, go for it. Again, no brainer.
- This one is more preference but i like to renew my ward and pop some kind of trinket/shield right before i mass taunt. It helps the healer not crap themselves and lets you unload aoes before dps starts to settle and you can better manage the aggro. Ex - HM BT, the first boss for instance.. That will give you the best idea of what i mean..
- Don't ever forget you have an interrupt and 2 stuns that work on the majority of mobs. USE THEM. Especially if you lose aggro and your taunt is on cooldown. Stopping damage from going to other players is your job... Making the healer fall asleep from boredom is also your job... Do those 2 things and you are golden in my book.
Anyways, time to get off the soap box i guess. I hope the above helps.