West - My wife and I guided for many years here in Colorado and hope our suggestions help.
Yes, there are some books on guiding, but a quick Google search did not turn up the titles. The Orvis Guidebook is a good start.
The best way to learn is to just do it. Hook-up with the best outfitter who will take you on and look forward to climbing the latter. (Meaning, senior guides will get the best clients & trips.) Everyone starts at the bottom.
Our philosophy on commercial fly fish guiding:
Guiding trout fly fishing makes us part entertainer, part educator (& skill / knowledge demonstration) & part therapist.
Entertainment - The best guides we know are very good communicators. They can read people and know when to tell jokes, josh with or rib customers, be quiet, etc. There is a guide out of the Vail Valley we call "Hundo Larry", cause he always gets tipped a hundred dollars, even when the fishing sucks. He just knows how to treat people well.
Educator - A good guide has to know everything about the river, the trout habits, the bugs and their hatch cycles, the best holes, etc. All this, or be a good bull-shiter. You also must have the patience to teach every type of cast or nymph technique. I made more good tips from teaching beginners how to do simple, but necessary casts. Mend early, mend often, is my motto. Having good gear & unique, hand tied flies are useful too.
Therapist - You will encounter all types of people, good and bad, mostly good thou. About half the people you will guide are stressed-out, and do not know it. You have the opportunity to influence their well-being, even if for one day. I love the challenge of the typical type A - "driver" business man who, even thou he is standing in the river with you, is still thinking about work. These people rarely take the time to smell the roses. I make it point to teach them how to handle and release a trout, turn rocks and look at bugs, point -out the pretty sunset, etc.
You will learn more about people and human nature than you ever thought. Very good life skills.
Oh, yeah, you will learn a great deal about trout & bugs, and make a little dough too!
Good luck & go for it! Mike