All of these things I didn't do, so do them and learn from the mistakes I've made:
1) Your focus is on teaching students music, not teaching music to students. They come first.
2) Remember that students have lives outside of class. Not every kid thinks band is life.
3) Communicate clearly, calmly and effectively with parents from the first instant you know you'll have their kid. Facts are good. Opinion and emotion is best kept to one's self.
4) Keep the principal in the loop on everything.
5) If you are an assistant, be in the other classes with the director unless told not to. Be a team player.
6) If a head director, be in the other classes as much as possible.
7) Building the program comes from the beginners. Seeing them on a regular basis is imperative
8) Don't be an a-hole.
9) Once you have schedules, get it on the master calendar at your school/district
10) Do your own budget. Don't let the business office do it for you.
11) Control your emotions.