There's no set formula for something like this. Here's what I'd suggest, but I may be wrong, so ask others as well: a short proposal, including an introductory paragraph that reminds the reader of how this got started, then the proposed business offering, then deliverables in detail, proposed schedule, and a section called "background and qualifications."
Just tell your story, and tell the truth.
If they're going to decide against you because you're new in business, that's disappointing, but you can't get around it because the truth will come out. So tell the truth, but then go on to why doing business with you is a good idea.
And if the college doesn't want you because your business doesn't have enough history, at least this standard proposal will be a good exercise. You'll be able to use most of it again.
Question added to topic Starting a Business • September 9, 2008
I am in the beginning stages of a vending business. How do I write a proposal to put my machines in a college that hasn't opened yet?
The contact person at the school advised me to provide as much information as possible about my business, including my years in business. I just started, and I don't know how to write a proposal that would prevent this from being a disadvantage.