Sometimes when you’re writing—especially if you’re writing fantasy material—the sheer pleasure of invention can become seductive and you start making up all sorts of groovy stuff: there are 18 ranks in the Air Command; your hero travels to an alternate universe.
Cool. Generate as much material as you like. But, when you review that material, make sure that it serves your story. Are all 18 levels of the Air Command necessary? Only retain the elements that have a direct impact on your plot.
And think your conventions through. If your hero travels to an alternative universe, what’s the portal? How does she get there and how does she get back? How does she explain her absences from her ordinary world?
Fantasy is fun—but only if it makes sense.