Yes, yes! I love fantasy stories. As many well know, I'm a huge Harry Potter fan. As of late I have also gotten into L.E. Modisette, Jr. He's an awesome fantasy author indeed. It's too bad movies haven't been made of any of them, because he is awesome. The Reclude series is more about magic from within using order, chaos, or a combination of the two. As the names suggest, chaos is more or less considered evil while order is considered good, yet order is "dark" while chaos is "white". In the Spellsong Cycle, it is about the magic of music, some music being "clearsong" or that which does not manipulate the living directly, or "darksong", which means more direct manipulation of what is living or was once living. In both series, magic takes a heavy toll on the wizard, sorcerer, etc. In his books, magic is quite complex as it is based in nature itself to a certain degree, while the Harry Potter magic is basically free of nature (aside from potions) and in generally increases the life-span of the witch or wizard. Thus, when deciding to write a story with magic, there are choices. But regardless, there should be rules and limitations of some kind, whether by some form of government or the heavy price one can pay for using magic.
I have a story in my head, but I do not know where to start when crafting the rules. Personally, I do not think magic in my magical universe should be life-threatening or life-shortening, but I see it being somewhat more limited than in the Harry Potter universe. Thus, it is somewhere in between. I do not think magic would be an inexhaustible force and could easily tire the user, because the magic is through the person in general. I know I need to do some research on magic theory as the basis of magic in my story and the rules that will be in this magical universe, but where should I start? Also, are there other great fantasy writers I should read (particularly any series that include a great deal of magic)?