Explain who the music program is for. Is the music program for elementary school students, or undergraduate students, or students wishing to pursue a career in music theater? You can also address the people involved in instructing the students. For example, "our committed teachers," or "experienced staff."
Explain what the goal of the music program is: It is not just to teach students music. Be explicit in explaining the impact that music learning has on the students and the community. Usually this is where the mission statement speaks of the broader impact music has on a person's life. For example, "provide a comprehensive music instruction" or "provide the community with outstanding performances." Express the long-term goals of the organization, because the short-term goals will change.
Request feedback from the school's governing body -- the board of directors, the school board, and the principal. You will also find valid input from the staff. You can use the current staff's activities, such as preparing for the Christmas concert, to learn about the greater direction of the organization, such as sharing quality music with the community. By doing it ahead of time you make people feel involved and avoid fallout after the statement is official.
Edit your mission statement, which should only be a few sentences. Remove extraneous words and passive language. Use descriptive phrases, not descriptive sentences.