I use these rules for grades Kindergarten all the way through Twelfth grade! They're pretty straightforward, and I think they cover all of the bases, every day, for everything from band through choir, and elementary music as well!
M - Make choices that help you and others learn
U - Use instruments and materials with care
S - Speak, sing and play only when asked
I - Immediately follow all directions
C - Consider others, be kind and respectful