Get hit and expertise capped, 7.5% and 15% respectively. After that it gets a bit finnicky, you want as much stamina and mastery as you can get essentially. The exact ratio will depend on what content your running, how many and what healers your running with, how competent they are, and how competent you are, the less threatening the content the less stamina you need. You want a big enough healthpool that healers never run out of time to heal you. Hit and expertise, and to a lesser extent Mastery decrease the size and frequency of those large damage spike events that kill tanks, more stamina means those spike event have to be bigger to actually kill you. Avoidance is a great stat for total damage reduction, stacking avoidance will greatly decrease the damage you take, which is great if healers are ooming trying to keep you up. Except healers really shouldn't be ooming trying to keep just the tank up.