If you're dealing with a world where magic is real, you can just go nuts, right? Wrong, argues Shadowrise author Tad Williams. In fact, you should use magic sparingly, and keep your world as grounded as possible.
The fine line between magic and just the incomprehensibility of the universe is big with me... I never use a lot of magic in my [writing], because I think it denatures magic, to have it be like hot and cold running water, and I want every time it comes up to be something that's exciting... If you're writing fantasy or science fiction, it's really hard to do if you don't know a lot, at least in a basic way, about how the real world works.
The whole interview is worth checking out. [The Link]