http://pwnwear.com/2010/01/01/two-blood-tank-extremes

Go there, check out everything and then whichever spec you go with follow his advice for spell casting priority. Make a castsequence, yes really, a castsequence for two rotations of runes. He has it all set up there so all you have to do is copy/paste(of course spelling everything out fully.) DK tanking is extremely easy and a castsequence works fine, I've tanked ICC25 raids with the bloodsequence. Make sure you dont include too many moves that require rune power though. It can hang your castsequence.