In order to give my Endhaven novels a distinct look and feel, I created a number of basic rules than inform the narrative and description.
Even though the Endhaven novels are rife with magic, I don't use that word anywhere in the books (although I do use the word 'magical' once) because magic doesn't mean anything. There is nothing unified about the forces of the world that makes the inhabitants think that magic is a single thing. The use of "magic" makes magic seem like a separate thing in the world when instead, magic is tied into all the simple things in the world. Because magic is so ingrained, its simply not seen as a distinct thing. Instead of using magic, people speak of secrets, techniques, skills, and knowledge. Magic is intimately tied to what you know and what you have developed. Magic is more of a relationship than an objective phenomena.
I also don't use the word "spell", because that narrows what you think of as magic. Because each area of magic work quite distinctly, there's no generic term for making it happen.
In learning about any one area of magic, you don't necessarily gain any understanding over another area of magic in much the same way that chemistry, engineering, and car repair lend very little to each other. Some knowledge of them does matter, but switching between them can't be assumed. Getting to know each area takes time, attention, and dedication.
Magic is pervasive in Endhaven stories, so much so that people just don't see it any more, much like you don't pay attention to sidewalks and plastic bags. Its very presence is assumed and ordinary. Because of its nature, it is also highly idiosyncratic, depending on what each character has learned, and the circumstances of their lives. Schan resurrect themselves, Astreans leap about in wuxia fights, and quite a few people escape death. Everything that exceeds reality is magic, and its accessed through a myriad of ways.
All magic is based on metaphors, and those metaphors shape how magic is expressed, and by extending the metaphor, show where that power can go. Metaphors hold the real power, and give me a way to describe them other than "she cast a spell," which as a writer, is perhaps the most boring sentence that I could write. "If she was the sun, if the light was within her, then it should show, truly show, so she opened up herself, let loose her soul, illuminating the world about her until her skin shown gold." The great thing about this approach is that I always have room to further explore the metaphor.
The goddess of Destiny is dead and has been so for many years. Prophecy is an unreliable art, more weather forecasting than knowledge. Predestination means nothing. The whole story always rests with the characters, with no one having any special place other than the ones that present themselves. The resolution of a problem always lies with them.