Explore the levels thoroughly, you may find hidden treasures. Talk to everyone. Many creatures are weak against some spells but strong against others. Flying creatures are weak against wind spells. Fire-dwelling creatures are weak against ice spells but strong against fire spells .
Insects are weak against crushing spells.
Water-dwelling creatures are weak against lightning spells. Be sure to get enough sleep. If you go too long without sleep you will lose mana points. Save the game frequently. Don't be afraid to leave a dungeon to spend the night resting at an inn.