Define the project. Write a list of what the project will entail. There are a number of ways to make this list. For example write down the goal of the project and the several objectives that will help you along the way. Think of these as a list of reasons for the recipient of the proposal to grant your request.
Determine what you need for the project to succeed. These are the things you are asking for in the proposal. It may be as simple as permission to proceed with the project, or in terms of a grant, it may be a sum of money. If the proposal is for an assignment, you may already have this defined for you.
Acquire the guidelines for your proposal. For some grants and other types of proposals, the recipient may only consider them if they have been presented in a certain format and according to certain guidelines. You may need to contact the recipient for this information, unless a professor or adviser can provide you with them.
Mark the deadline on your calendar. Consider whether you have the time to complete this proposal before the deadline expires.
Read some example proposals. Style for proposals changes often, so make sure you are familiar with the current style. Ask a professor or adviser for examples of some successful essays.
Write a first draft of your proposal. Lead with the goal of the project and the other objectives. Make a clear and concise argument as to how you will achieve the goal. If there are other benefits to your proposal, include and highlight those. Clearly identify why you need their assistance.
Give your proposal to a trusted friend or adviser to read. If they are not familiar with the style, ask them to read an example or two to get a feel for the style. Have them make edits and suggestions and return it to you.
Make the changes suggested. Repeat the process of editing and revising as many times as possible, and with a number of different editors. Try to complete this within at least a week before your deadline, then leave the document for a day or two.
Reread your proposal. Make sure it still flows and sounds correct. When satisfied, mail the proposal to the recipient.