Check the word count that is required for your proposal. A Master's proposal may have a shorter word count than a Ph.D proposal.
Focus your ideas into a single theme. Proposals are sometimes not accepted because they try to do too much, rather than focusing well on a clear area of inquiry.
Identify and describe the area of research that your work fits into. If there are a group of writers who have dealt with similar subject matter to the one that you want to study, describe how your work fits into this group, and how it departs from it into your own original perspective.
List and briefly elaborate on each of the areas of inquiry you intend to research. Write about why this is important -- not just to you but to the field of philosophical research. Describe what it is about these questions that makes them compelling and relevant outside of academic research.
Explain how you will research these ideas, listing the methodologies, surveys and other research methods you will use.
Write several drafts until your proposal is as clear and concise as you can make it. Have a non-academic friend or relative proofread it, to make sure that it is reader-friendly and not too cluttered with jargon. Also have an academic supervisor proofread it, to make sure that it is written to the required academic standard.
Give it a title, when you are satisfied that it is finished.
List all primary and secondary sources at the end of the document, using the style guide that you are asked to use -- or that you choose, if permitted.