You can look online for sample proposals that you can work from, in many cases you will be able to download a template that you can work from. You will most likely find that there are dozens of sites offering hundreds of different templates to download. It may take a while, but you will find that there proposal forms that will match almost any need including yours. Take your time and select the one that best suits your needs.
You may even find a form that has already been completely filled out that will allow you to see exactly how a successful proposal should be written. In most cases the forms will include spaces for you to add pictures, charts and graphs as necessary to explain your proposal in such a manner that makes it much easier for the reader to understand your proposal. In many cases the more detail used to explain a proposal, the better the odds are that you are going to be submitting the winning bid.