Shit i'm too late, all the niggers (Justin, Iyona, Tuvok and Devlin mostly <3 ) gave all the yummy advices already...
Well i'm just gonna give you a picture to emphasize the UBER TANKING ADDON :
Tidyplates + Threadplates
Here's an old UI of mine. Dont bother with the bullshit, raid UI and talent bars. Just look the mobs lifebar.
GREEN = GOOD, I GOT IT ON ME.
RED = POTENTIALLY BAD, ITS NOT ON ME WTF. Now, in a raid there may be other tanks so usually i just mousever the mob and see who he's targeting. In a 5m situation, you can be sure that if it's red, it's on a dps / healer and it's bad. That's the proper time to taunt that mob back.
Try it, love it !