Dk tank, assistance in equipment

Hi,

My dk tank is: The World of Warcraft Armory.

I thinking about the cup of expertise, the avoidance,HP...etc, but not to do.

I recommend? expertise climb up to the limit, and my life decreases or my avoidance.

I tank nax 25 and ulduar 10.

Very thanks.

P.S.: I feel sorry for my bad English. Im spanish :P.

don´t worry about expertise, you don´t need that for the runestrike that gives most aggro... but you need as much avoidance as possible, preferebly dodge rating on the gems to make your runestrike procc as often as possible