First Strike Finisher
First strike will often allow you to kill a monster you couldn't otherwise beat. Cast it just before the final blow, and the monster gets no retaliation hit.
Hitting a monster with fireball before combat will often reduce the number of hits it takes to kill it.
With very few experience needed to gain the next level, you can fight a tough monster, and then when you can't fight any more, kill a low-level monster in order to level up. This will restore your health and mana without healing the tough monster. You can then go back to killing the tougher monster with full strength.