I do this with my HS band every four years. You’re going to love it!
Do you have someone in mind? Before you contact them, a few things to figure out are:
How much can you pay them?
When will you perform it? When do you want the completed score and parts so you can start rehearsing?
Do you want the composer to come in to work with the kids? How many times? A day here and there, or a short “residency?” If they stay for a few days, can you pay for their lodging and meals? Travel expenses? If they’re local, you won’t have to worry about that.
How long of a piece do you want?
Will the composer be willing to work within your technical limitations? Have they written for young band before? If not, they might need specific guidelines about range, keys, rhythms, etc. It’s not safe to assume that even a great composer will know that a B natural is much harder than a Bb for young clarinets, etc.
Once you know what you’re asking for and how much you can pay them, jump right in and contact someone. Once they agree and you talk about expectations on both sides, you’ll probably want to draw up a simple contract. Feel free to email me if you want a copy of the one we use.
Commissioning new works and working with composers is my favorite thing that we do in my program. Have a great time, and if you feel comfortable, please post again about your experience.