Books: everything about the music business, everything. Books on just business. Books on strategy. Books on wars. books on relationships. Books on philosophy. Books on history. books on everything that might be useful. My favorite book is called "The Book of 5 rings" by Miyamoto
Musashi. Books are not doctrine, take pieces from them and allow them to fit you.
OTHER PEOPLE: just simple observation. sometime questions. But watching people is the best thing. I study people, I really do. I read people. I can tell if some one is bullshting before they say a word. I watch their posture, eyes, hands, stance, lips. these things speak louder than their words, you just got to learn how to listen. learn form people at your level or one up. don't try to learn personally from some one way above you. one step at a time. also the music industry is just like high school. just like it.
BY DOING AND FAILING OR SUCCEEDING. make many mistakes when you are just starting, if you screw up you can't fall. but when you start to climb, falling can kill your career.
SCHOOL Workshops seminars, etc. anytime you are able to get near someone who is more experienced do it, learn from them. even if it is for a few hour.
Your normal life, I'm from chicago. i was homeless when i graduated high school. I learned how to hustle very well, very well. I later was in the army, I learn how to manipulate systems from them. Take what you learn in your life, and apply it to this
internet: I'm giving you advise right here, on the net.