The idea is to spam Q on as many heros as possible. It steals their strength attribute which will take their HP and give it to you! :)

Sit there and spam Q on 3 or more heros and watch and they sit confused on how to kill you.

The tombstone spell is your second best, hide it on the high ground if possible. The zombies will continue to spawn right on top of enemy heros within AOE. If they leave the AOE or destroy the zombies / tower it is worthless.

Your ultimate will turn you into a serious boss to better utilize your other spells. I would pretty much keep this off cooldown and cast it whenever possible.

The soul rip spell is good but not your best. Think of it as a stick that anyone can use.