Each boss has a creature type. Stacking damage dealt and damage recieved for the boss creature type is a good way to take them down with ease. If you're lucky you can get gear with dmg + and creature dmg +. A whole set of gear like this should be used in 5 of your equipment bags if you plan on playing infernal mode seriously. Also keep in mind these bonuses are further increased by potions that raise attack, as well as other skill and equipment bonuses. There is no cap on damage dealt, so get it as high as possible.