I had a hard time when I started tanking heroics in blues, but here are some tips:
Get the group to work with you to help keep you alive. This means asking the warlock to break out his imp for the huge stamina buff instead of sacrificing his succy or whatever. Him doing leet dps doesn't mean jack if the tank is dead.
On hard hitting mobs (the big pairs of naga that can't be CC'd in Slave Pens come to mind) have a warlock use Curse of Weakness or a warrior use Thunderclap/Demo shout to reduce their AP. It makes a big difference. In the case of CoW, have the lock put it up on the target that will be killed second, so that you get more use out of it.
Ask rogues to be on top of spell interrupts (Charged Fist anyone?) and also ask them to use kidney shot instead of other finishers on particularly hard hitting mobs. A 6 second stun that halts incoming damage to the tank contributes a lot more to a smooth run than a 2k rupture or eviscerate.
Basically, approach it from the angle that if you all work together as a team instead of focusing on "big numbers woohoo leet dps" it can be a nice smooth run




