1. Do Your Best. Don't try to be the best, you'll end up with an out-of-control ego, no friends and a broken heart. Just, be your best. Always strive towards greater happiness for yourself and others, and with that intention, continuously work towards a great understanding of both yourself and your surroundings. A personal best can be anything and life is full of teachers help one reach their potential.
2. Be Sincere. Don't be fake, phony, false, or do it just to pretend. If you are playing music to get rich and famous, hoping or believing that you are going to be the one to make it big, remember the cold hard fact that the odds are against you. There are so many musicians out in the world "trying to make it," and there aren't enough dream jobs to go around. Music is a beautiful language, and like all creative mediums has an incredible power. Make your art - whatever that is, for the sake of making that art, do it because you enjoy it. If other people enjoy it - consider sharing it with them. That brings us to our third golden rule:
3. Be Realistic. All three of these rules apply to being a good musician, but I believe they also contribute to being a good human being. Being realistic means having unattainable goals, but it also helps you get behind your goals to take a look at your motives...
At this point it is very easy to get philosophical about what our purpose is and the meaning of life... What are our sub conscience motives, and how do they relate to our conscientious motives..? However, let me leave you to ponder the universe for yourself with one of my favourite quotes, one by Picasso:
The purpose of life is to give it away."