Whether you want to find a sponsor for an individual, a sports team, an event, art gallery, festival or a charity organisation, you first need to write a sponsor proposal. Sylvia Allen in her book "How to Be Successful at Sponsorship Sales" (2010), notes that there is no such thing as a generic proposal for sponsorship investments over £650, and that sponsor proposals should be tailored to the specific audience. Still, she also recognises that sponsor proposals have many commonalities.
Identify the audience who will read your proposal and make the sponsorship decision. It is one thing to address a sponsor proposal to a multinational corporation and another to a rich uncle. Depending on the audience, determine the writing style and whether you can use any technical terms -- you can use them if you and the audience are in the same industry, for example.
Set your objectives in one or two sentences. For example, "I am writing on behalf of Green Treehuggers Association to request your company to sponsor the Save Nature music event that will take place in Springfield on 15 March, 2011. The amount we need to raise is £6,500."
Provide detailed description about the sponsorship and how the money will be spent. Break down the costs in as great detail as possible. If you are organising an event, tell what the event is, why it is important, how many people you expect to attend and what agenda you want to raise. Also, include information on your other sources of finance, if appropriate -- other sponsors for example. Be advised, however, that some individuals or companies may not be willing to co-sponsor something with an "evil" company, such as a tobacco or alcohol firm or another bad corporate citizen (for example, BP after the 2010 spill in the Gulf of Mexico).
List the benefits and advantages the sponsor will get from funding your cause. Those may include higher brand awareness in the firm's consumer base (e.g., young people), higher general publicity and increased sales.
Provide the methods by which the sponsor can -- or will be able -- to verify the information you provide in your letter, particularly the financial part. If possible, offer edited or unedited copies of previous sponsorship contracts and receipts verifying the expenses you anticipate to incur.
Include your contact details, such as address, direct telephone number and e-mail address.
Review and edit your proposal. Also, give it to someone else to proofread.