practice,practice,practice,.....
avoid standing still too much
against melee opponents:fire at max range
against casters:get imp. counterspell
use frost-nova to:
-stop mobs chasing you
-pin mobs in place around your tank (usually works)
-buy time and distance in combat
get first-aid!!!
never forget you've got will of the forsaken
sheep when fighting multiple mobs
eat and drink after each fight (when solo)
know when you've got dangerously little mana
meditate on a good build
i advice going arcane first so you can get imp. Arcane Explosion, imp. arc. missiles,imp. counterspell and evocation (all worth it imo)
and basicly,just get the feel of it
oh and never forget:you wear cloth
ok thats as much as i can come up with....
maybe a GOOD mage should post here to give additional advice