Some tips is to bring dirty waters with you and toss em on tough enemies to lower their lightning resist.
Train your curses, they can be very handy. Like nixing their resistances, and the higher lvl mobs need their resistances nixed unless you want to spam magic dart till you're sick of it. Slowing them down so you take an extra turn or 2 over them, combine that with speed spell for even more turn advantage.
Always stock short teleport and teleport, they're life savers. And use the short tele to move out of melee range, it usually puts you down still in visual range, but a bit far for their melee. Also dark eye is a mages best friend when fighting other ranged stuff, blind sucks just as bad for the npcs as it does for you. Silence too works good for the casters if you can't get dark eye to blind for some reason.
And if you do decide to be a caster, the mages guild is pretty much a requirement. The bookwriter in there makes the mages life so much more bearable.
I can say I'm having the most fun with my wizzy right now, vs the other chars I made in the past.
Edit: Breaking the post up so it's a bit easier to read.