At low levels you can get away with only meteorstrike. Once you start getting into the 20s, picking up some proficiency in lightning will come in useful as you will be finding enemies who resist fire.
Life leech can also hurt the big baddies quickly if their spirit resistance isn't high. Freeze also works quite well(perhaps too well).
Both spell shield and aura of guarding are useful until you get into the end game area when you can use a lot of gold charms to increase your hp and mana.
Limbs of lead is handy (can't be resisted) and works well with hellspikes. When you get to the end of the game, divine death + curse and temporal storm + hellspikes are really all you need. Elemental strike is effective with curse and enemies with low resistances but is costly in mana.
Level 5 hellspikes is one of the best spells you will get. I use that mercilessly even at the end of the game because only a monster's armor class will lower its damage. Enemies at the end tend to have very high resistances across the board. You can curse more than once to lower them but that seems kind of cheap that you are able to do so.
I avoided the summons because they are fairly weak and seem to steal experience. You also don't really need meat shields because most enemies are slow and you can immobilize/slow the faster ones if needed.
I recommend picking up evade arrows and elven sight to take less damage from ranged monsters and see further respectively.
