One vital element of any good fantasy setting is, of course, magic. It’s basically what separates the genre from realistic fiction and action/adventure. Not that it really matters, most genres are so closely lumped together these days that the libraries don’t even bother separating them. My book(which, technically, is both sci-fi AND fantasy, at the same time) is on the shelf between a whole mix of genres. Author of the Gust frequently gets mistaken for fantasy, despite including no magic(and sort of technically being sci-fi, kind of).
But it’s not enough to simply create magic; you have to assign a cost to it. Failure to do so is the cardinal sin of the fantasy writer. Magic without cost becomes droll and thoughtless; and most importantly, it makes what could be a major element of the storyline just another plot-forwarding device.
In a certain strangely popular fantasy universe you’ve all heard of, the author commits this sin over and over again. In her world, magic is as simple as waving a wand, every kid can learn the instant-death spell with ease. With every person in the “wizarding world” carrying around a wand and knowing the magic wards to kill people, you’d think there would just be a constant stream of bodies EVERYWHERE. The river Thames should just be chocked with dead! London should be like Los Santos from the Grand Theft Auto series: just a constant blood-bath.
Video games and table-tops solved the costing problem long ago; they used a simple ‘point’ system. A mage has a finite number of ‘mana points’ that can be spent to cast spells. Unfortunately, this sort of thing doesn’t translate particularly well to writing.
There is obviously no “right” way to creating your own magic system, and copyright law sort of demands that we each at least try to come up with one that’s vaguely unique. Even if it’s as simple as magic beads that have to be spent to cast spells, that’s still miles better than no system at all.
The system does not have to be complex. Terry Pratchet, author of a fantastic series of highly comedic fantasy novels you should definitely read, had a system that was laughably simple. But since magic wasn’t the primary focus of his stories(humor and characters were) it worked quite well.
So take some time, jot down some notes. Really muse about it for a long time. There has to be a cost and an underlying system associated with magic. Even if it’s so complex that it barely presents itself in the series(such as the works of J.R.R. Tolken), you need a set of rules for your magic to obey.
In The Course Books, I equate magical strength to physical strength. E.G., casting a great spell is akin to lifting a great weight. This example holds true if you get smart about it, a weaker mage can cast a more powerful spell by using the magical equivalent of a lever. Magic even has laws, much the same as physics, and the two main characters devote themselves to determining these laws. By bringing scientifically rigorous experimentation to the field of magic, they are able to eventually cast extremely powerful spells.
Many authors over the years have invented a wide range of very unique and interesting systems. One method that seems to work is equating your magic system to something you know well in the real world. In my series, I used physics. Other authors have used computer code, cooking, or even a simple logic process. Spend some time thinking about it, and decide on one that works for you.