Warrior Tanks!! What's your best tip?
My best tip is this (in addition to all that was said above):
Relax and do not be a dbag.
So many tanks out there get offended easily by people making mistakes or are just plain Prima Donas. Do not be like them. Like someone said, the tank sets the pace, but he can also set the mood for the run. Make it an enjoyable experience for your group and people will want you for their runs in the future.
The "Relax" part will allow you to be more aware of what is going on around you, and make the whole tanking experience enjoyable.
Reality is a matter of perspective.