Here's a guide I'd recommend to anyone who wants to tank as blood. It's very detailed, covers pretty much every aspect of blood tanking. The guy writing is a well known dk tank, and is very knowledgeable.
http://pwnwear.com/forum/death-knight-tanking-guide-blood-t703.html (http://pwnwear.com/forum/death-knight-tanking-guide-blood-t703.html)
This one is more for current blood tanks at 80. There's alot of info here, but nothing detailed. Good if your looking for a quick answer.
http://pwnwear.com/forum/death-knight-tanking-guide-t711.html (http://pwnwear.com/forum/death-knight-tanking-guide-t711.html)