Go to college and become a grad assistant for the coaching staff. That is a few years away for you but is often a fast track to learning and getting to know the right people. For now, read about it as much as you can and see if you can help out a local hs staff if you aren't playing football. See if you can voluteer for a youth program. Learning how to fit and repair equipment will help you get a foot in the door as well.
Also, and this is very important, you only think you know all the basics. I used to think I knew alot and then I learned that I knew nothing. A decade of coaching and I still feel the same way. As you peel back the onion you realize that the layers are endless. One could write a book just on the first 2 steps of an offensive lineman. Literally. That is basic stuff. Go into it with an attitude that you don't know anything about the game. Realize that you can learn something from a youth coach with 1 year of expreience as well as Bill Parcell's or Bill Walsh. Oh, and books by those 2 guys are highly recommended. Be humble but aggressive with your learning approach
As far as a reading list be careful. Jumping into advanced scheme will blow your mind at first. What you consider advanced and what others consider advanced are 2 completely different things. You have years to learn advanced scheme. Most hs coaches don't truly understand advanced scheme. I would stay away from scheme based books for now and stay with books written by coaches about coaching and books about fundamental skills. We could give you a list of books about advanced scheme that would blow your mind(heck, they blow my mind and I have a decent amount of experience and am exposed to very knowledgeable hs coaches on a daily basis) but that won't help you much.
Remeber coaching football is not about scheme. It never has been and it never will be. Coaching fundamental skills at a high level is what makes a good coach. Running a simple pass concept like Smash is worthless if the qb reads, steps, throwing technique, and the wrs reads and route running aren't correct. Then don't forget pass pro or the qb is on his back. Same thing with running a basic power play or inside zone. The fundies have to be right for the play to work.
Learing as much as you can about coaching the oline will do wonders for you. Good oline coaches at every level are hard to find. Plus, you really start to get a quick understanding of the offensive and defensive game from the trenches. Many people have no desire to coach the oline. Once you dive into it the line becomes really interesting.
