My favorite form of magic for stories is based on animist religious beliefs. To wit, everything has a soul. Magic, therefore, is simply knowing how to ask a thing properly to do you a favor. What kind of favor a rock, fire, or cloud might do for you is based on its nature, as is what it might expect in return. The challenge to magic is partly in being able to supply what the spirit you address desires, but mostly in being able to communicate with it.