Hint: Two words of advice: Turn Undead. If you're planning to fight through the Barrows or the Haunted House, you're going to need that spell. It's a good idea to have someone in your party who can cast it.
Hint: If you're wondering how your mage can do more damage per round, try studying Earth magic. The Blades spell, which comes at Expert level, can do more than 40 points of damage in a single cast.
Hint: Range striking is the key to survival. All of your characters should have the Bow skill and carry the best Longbows they can find. If you have enough space to maneuver, you can take down a really big monster just by running 20 yards at a time and then turning to pepper your opponent with arrows.