I'm a big believer in Web and Fireball. Once you get the spell, just use circle of death to get rid of lower level enemies. Then have the cleric cast protection from arrows on the mage, so that he doesn't get hit by those pesky arrows when he's laying down the webs and blasting with the fireballs. Icestorm works well for those who have resistance to fire, so I cast it occasionally, just to keep the opponents honest.
I'm liking the game, but are the 10-12 places on the map the only places in the whole game? If so, I'm way over halfway done. It could be you have a whole other set of maps too, I don't know. I'm in the hill giant fortress right now and I'm slaughtering them because they can only fight one vs my two
I crafted the highest constitution equipment that I can so that my two fighters and my cleric have well over 100 hit points. My mage just hides if melee approaches.
I use two wands-heal critical wounds and fireball for most large battles. I don't bother with spells against hill giants. I just let the meat shields take care of them and let the cleric heal their ouchies, afterwords.