There's a lot of valid tactics in this thread for WAR. I love the class for it's versatility and it's pretty much the only thing I play. The only things I can recommend are:

Defiance: On or Off for me depends on how good the healer is and if I can keep enough hate. Additionally, during BC Turn 2 or Ultima HM where I need to swap with another tank, I turn on Defiance when I'm tanking and then off when the other guy is about to take over to make it easier for him. That's not to say you can't do a full dungeon with Defiance off. I've done WP and AK that way.

Holmgang: Useful when you think you're about to die since your HP can't drop below 1 or need to hold something in place. Keep it handy.

Aside from that, learn to use your self-heals, you can figure out what tactics work best.