Max Raise Skeleton, Skeleton Mastery, and Golem Mastery. Put one point into Summon Resist, Clay Golem, Decrepify, Amplify Damage, and Corpse Explosion. Get an Act 2 Mercenary from Nightmare (once you get there) with Might aura (which is Offensive style).
You will summon your 10-12 Skeles and a Clay Golem (who is just there to slow down bosses), then Amplify Damage on all monsters and as soon as one has died, use Corpse Explosion to kill all the others. On bosses, throw Clay Golem right on top of them and use the Decrepify curse - they will literally barely be able to move.
Other than that, just focus on your resistances and magic-finding - stay away from the monsters and you will be very safe.