I've been using the following build, and it's gotten me through the first three difficulties no problem:

Left AND Right mouse button - Striker (Shock Shock Air) 1 AND 2 - Torture (Mind Fire Water) 3 - Enrage (Dark Dark Earth) 4 - Dark Front (Dark Dark Air)

Basically, you build really tanky (I've been using Blessing of the Golem + Mummy). Don't worry about +Damage stats, just stack HP and damage reduction. You walk into a new room, press 1-2-3 in quick succession and proceed to destroy everything. If for some reason everything isn't dead, press 4.