I'm lvl 21 with:

Heal - 5
Frostbite - 1
Lightning - 1
Resurrect - 1
Firestorm - 5
Ice Storm - 0
Drain Life - 3
Weakness - 0
Nightmare - 0
Magic Shield - 0
Blessing of Vitality - 1

I currently have 4 skill points to spend but don't know where they are best used. Please advise.