Think of the Project Overview as an Executive Summary (the busy executive probably only has enough time to read your Overview - not the entire proposal). Be specific and concise. Do not go into detail on aspects of your proposal that are further clarified at a later point in your proposal.
The Project Overview should "paint a picture" of your proposal in the mind of the reader. It should establish the framework so that the rest of the proposal has a frame of reference.
Use the Project Overview to begin to show your knowledge of the organization from which you are requesting funds. Key concerns of the funding organization can be briefly identified in relation to your proposed project.
If you will be collaborating with other organizations make sure some of their interests are also highlighted in the Project Overview. This can assist in strengthening the collaboration by recognizing them at the very beginning of your proposal.
The best time to prepare the Project Overview is after you have completed the entire proposal (and you understand all aspects of your proposal very well). Let the Overview be your last piece of writing and then insert it at the beginning of your proposal.
Try to keep in mind that someone will be reviewing your proposal and you would like to have this person be very positive about what you have written. The Project Overview will probably form a strong impression in the mind of the reviewer. Work on your Project Overview so that you can avoid giving this person the opportunity to say things like:
Not an original idea Rationale is weak Writing is vague Uncertain outcomes Does not have relevant experience Problem is not important Proposal is unfocused Project is too large.