When you get to the Wizzrobe type boss simply use the shield and reflect spell and sit in the bottom left corner of the screen and duck. His waves will kill him and he'll never be able to hit you because of your positioning.
When you pick up a red potion bottle or recieve free magic from the old ladies and you're in need of some health fast, simply use the heal spell as soon as the magic meter starts to grow to refill your health. The magic meter will continue to go up making it very handy in dungeons.
When you get hit and you land on the very side of the screen you won't die! Just stay on the side of the screen when you health is at 0. Fight to get some goodies. When you're done, run to the left or right side of the screen and you will escape.