Young man, read everything you can get your hands on, sixman, eleven man, biographies, How to books, treatises on war strategies and tactics, offensive books, defensive books, Sun Tzu, Vince Lombardi, George S. Patton, Alexander the Great...
Seriously, read everything you can while you can. Last June I read "Football For Dummies". It strengthened my perspective in a couple of areas. But a quick word of advice--stop reading in time to gather your thoughts and solidify your style and philosophy. Too much info will dull your wit and make you wishy washy. I stop studying each summer by July the first. That gives me a month before two-a-days to plan.
And never forget this old saying:" When you think you have it all figured out, you don't". So stay humble and mentally flexible mixed in with a measure of discernment. Throw away what does not work against the best teams.
If you want to learn it fast, find a successful coach and be his assistant for two or three seasons. That will save you six or eight years. Most of us don't have a coach in the family to learn from.