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. Can be used with first strike to take on otherwise dangerous foes without taking any damage.
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.
If you have enough attack to do more damage in one hit than your enemy is able to regenerate in the time it takes you to regenerate the damage that he does with a single hit, you can heal between attacks and still be able to have a net effect of his health decreasing.
Casting poison on a single enemy and then alternating between attacking it and exploring allows you to take on enemies that would otherwise outlast you in a fight. If attacking with magic you can use this technique to beat a foe that would otherwise kill you with one hit.