Belt: Get a Witching Hour. Single biggest upgrade for you I think.
Helm: Probably Zunimassa's Vision. Crit chance if you can afford it otherwise get the Int as high as you can.
Armor: Zunimassa's Marrow. Best for the price.
Consider Lacuni Prowlers for the movement speed.
Look for pants with all resist, 150+ vit, and int. They're pretty cheap.
Definitely change your mojo. A decent Thing of the Deep is very cheap, or an Uhkapian Serpent if you don't care about the pickup radius. You'll have lots of mana regen already from 4pc Zunimassa set bonus if you've followed my other advice.
Try to get gloves with crit damage as well as crit chance.
Try to get an amulet with crit damage as well as crit chance.
Try to get a ring with crit damage and crit chance.
Change your skills. Look around the forum - there are lots of build suggestions, and there are lots of problems with your build.