Wards are in the restoration school. Use them against the mages. Turn undead is great in the old ruins. Make sure you have them on favorites so you can swap them out quickly with your heal spell.
This is what I found to be the most effective method, actually. Healing doesn't give that much XP later on, and I always disliked to intentionally hurt myself to be able to heal, anyway. That's grinding, which I already have to do with the crafting skills. Using Wards and Turn/Repell Undead make for much more natural leveling while you're actually playing and they give a decent amount of XP. I admit, though, that they are not necessarily the most practical spells for everyday use, depending on your type of character.