-Focus Target high dps/taunt that mofo
-Use your cc's when someone needs it, not like youre giving away candy
-Watch enemy movement...especially melee-You can usually get a swap off before someone starts taking damage if you can judge where someone's moving.
-A lot of people say Aoe taunt on CD...I like to think of it as a cooldown I can give my teammates when they need it. 3 people jump on my healer BOOM damage reduc.
-Try not to waste taunts by stunning them with a taunt up
And realy just know what your class can do and practice till its second nature...Every match you'll come across a situation where you can think to yourself "Hmm maybe I should do this and this when darthsithlord uses this move" So just try to learn something new every game.
Its early/can't think or type but I wanted to keep you company