Try to let the spell hit its target before casting it again. If you want to get to a specific time of day, you can sleep at an inn several times in a row. If you don't leave the inn, you won't have to pay for another key. 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.