I've learned a lot about the supernatural by reading White Wolf books.
No, wait, let me explain.
It's so much fun to mock people who play White Wolf and think they know everything about "real" vampires, werewolves, fae, wraiths, or, yes, mages. Take a look around for it, you'll see it all the time. Trolls on www.sanguinarius.org announce "Oh, you're just playing too much Vampire". Posters on www.were.net guard against using too many Werewolf terms in describing themselves. The worst insult one can deliver to a poster on an otherkin list or board is "roleplayer".
I have been roleplaying for about eight years now. I have also been practicing celestial magic actively for several years, and I've been doing magic pretty much all my life. I have done a good deal of traditional research into both celestial magic and magic in general, to the point of pursuing a degree in religion. However, having never "grown out of" or "gotten into" magic, my many of my resources for learning magic have been nontraditional.
In Mage: the Ascension, a White Wolf game in which the main characters are magic users, people who can use magic are called "awakened", and normal humans are "sleepers". The other day I came across the idea of a child mage in the player's guide. It said that most mages see a child mage as one who awakened early, but in truth children are born awakened and later go to sleep. This is why a child's games can seem to real to them even though they seem aware you don't believe in them. Someone who never went into this metaphysical sleep, it is suggested, would view the world very differently than one who awakened later.
When I was young, I saw faeries. I read faery tales to learn how to interact with them. I learned many important lessons about dealing with fae from those stories, and they probably saved my rear more than once in dealing with them. Many of the magical techniques that are most familiar to me today are things I learned when I was young. I am not ashamed of the fact that most of my habits and techniques come from fiction. I find that fiction can hold just as much truth, if not more, than the new age section of Barnes and Noble or the rare occult book collection at most universities. I'm not talking about casting spells from Harry Potter or Dungeons and Dragons. I'm talking about mindsets and terminology.
I first read Madeleine L'Engle's A Wrinkle in Time when I was eight. It was a story that struck me as painfully, beautifully true at the time. It is still one of my favorite books. From it I learned about tessering, a way to move through space and time that I use for spirit travel. I also learned that the relationship between magic, religion, and science is much more complicated than most people realize. From it's sequels I learned about mitochondria, cherubim, echthroi, nephilim, and ogham. It gave me ideas to pursue in time travel, and a useful rune of protection.
The other books that made the greatest impression on me were the Chrestomanci books, by Diana Wynne Jones. These books explain the concepts of alternate worlds and different theories of magic in such a way that preteens can understand them. I learned dream travel and song magic from her books, and explored a number of philosophies.
I learned to see the magic around me as a web from Searching for Dragons. I learned to channel and weave energy from the Thread that Binds the Bones. I learned to use madness from the Malkavian clanbook. I picked up some Internet sorcery tips from the Virtual Adepts. I studied how to better hide myself from the Changeling sourcebook. I understood the essence of magic and energy by playing Final Fantasy 7.
Sound silly to you? Maybe, but I am not ashamed to admit that I have learned many things about magic from fiction. This viewpoint tends to be frowned upon by serious students of magic. There is "real" magic and there is "roleplaying" magic, and never the twain shall meet. But magic is fluid, based in will and perception as much as reality, and fiction is even more so. The study of magic is often a search for truth. The beauty of fiction is that it is truth, even if it is not fact. When the goal is the same, I see no reason why they shouldn't share some steps along the way as well.
Magic is an art, using to tools of will to paint on the canvas of reality. If you believe in it, odds are good it will work. It doesn't matter if some textbook says it's not real art. If it lets you paint the picture you want of reality, then it's an effective tool. People can say it's fake all they want. If it's working for you, their opinion can't change that.