The representation of magic in fiction, whether it’s in the fantasy genres or not, requires a deft touch. This is especially true if, like me, you aspire to write literary fiction and want to write a story that’s believable enough that your readers can happily get lost in it.
Method One: Just let it be
There are basically two ways you can go. First you can just present magic as a fact without trying to explain it. Treat it like just another part of nature. The best example of this I can think of is Glen Cook’s Black Company books.
That doesn’t mean you can do anything with the magic. It quickly becomes either boring or irritating for the reader if your magic users can do anything. Boring, because there’s never any real suspense in your stories; irritating because they will notice when you try to create suspense and fail because your character inexplicably don’t turn to magic for the solution.
You need to set ground rules—including restrictions—and stick to them. These rules don’t have to make an explicit appearance in your story, but you should have them clear in your head when you are plotting and even more so when you are writing the actual narrative.
Having a good explanation as to why this or that task can’t be done using magic should be there to be written or spoken by a character if the moment demands it.
Method Two: Lay out Magic’s Laws
The other approach is to make the mechanics and physics of magic explicit in your work. This approach is riskier for two reasons.
If you fail to make the rationale behind magic convincing, you’ll lose the reader fairly quickly.
Also, your story is going to more about magic than it would be if you’d taken the first option. Your plot may tend away from the route you’ve planned for it; if you resist this trend, your reader is going to wonder why you spent so much time explaining magic when it played so little role in your story.
The benefit of this second way is, if it works, you’ve pulled the reader that much more deeply into your world. The best example that comes to mind of this approach is Robert Jordan’s Wheel of Time. Despite its flaws, Jordan did an admirable job of creating a compellingly believable magic system in his series.