It just totally depends on the nation I'm playing. Right now, I'm Vanheim, and those Elven "Van-" wizards are almost indestructible. When I know I'm likely to win a battle, I'll often cast a defensive spell on myself as well--Air Shield, Mistform, and Ethereal Body (?) are all good low-fatigue spells that protect against your average boo-boo. That failing, the Lightweight or Weighless scale mail are pretty good for fragile mages, if a bit expensive.
It costs you the "Initiative" of getting a first spell off, but unless you're in an arms race with another spell-caster, it's the best way to preserve your caster. And, frankly, in the battles where you outgun the opponent, you often want to let him get a little closer to ya first!
Alternately, you can just summon yourself a Troll King and go happily about your business!
