I will try to give my 2 cents from the perspective of a parent since I feel we are part of the equation.
Strong Middle School Infrastructure for Music - One of the things I noticed is that they did not just teach my child to play their instrument, but to understand and instruct on the music theory first and than addressed the instrument with proper care, handling and simple maintenance.
Private Lessons - if you cannot afford, than work with the other students who do get it and learn from what their private lesson teachers provide them.
Parental Support of the children, programs and directors (Both at the Middle and High School Level) - As many parents who have the ability to donate their "time" and "resources" is critical. Resources does not mean just money, but also talents. Believe me, I have provided help in areas where I felt I had no ideal what I was doing so talents can be hidden by effort!
Practice, Practice, Practice
Winning or placing is not the goal, performance excellence is the reason you do this from an individual and ensemle. It shows love for your craft and not the need to be recognized.
The children taking personal responsibility for their actions and respecting their student leadership as well as parental leadership.
Respect for other winning programs and learning from their successes. I am sure if you interviewed a band director and the kids in their programs, in most cases they are more than willing to provide their insight. This is about humility and not thinking you know the way, the winning directors and kids I have met are full of humility.
A system based on competition can thrive as long as everyone understands in our culture of subjectiveness that life is not fair and if you know you did a great job and did "ALL" you could do, than you are successful.
I am sure their is much more, I just gave my perspective as a parent.