A few basic principles for writing a proposal, many of which I got from Scott Gaudi in Astronomy:

1. Make sure that the first sentence of every paragraph summarizes the entire paragraph, and that 

2. All of the important points are covered in the first sentence of some paragraph.  That way a busy "skimmer" gets all of the important points.  Use italics to make the most important points jump off the page.

3. Say up front, right away what you want.  Don't take several pages to build up to it like you would in a paper.

4. Make the case that you (or your group, or collaboration) are uniquely qualified to carry out the proposed plan.

5. Make the case that the proposal is timely

6. Make the case that if they do not fund you to do this now, then the world will fall apart.

7. Identify the strongest weaknesses of your proposal and address them up front.  You can even turn a weakness around and make a major objective of your proposal to fix it.

8. Demonstrate that you are already doing what you are proposing to do.

9. Include a table showing what you will do each year, including what you will publish and when.

10. Leave no ambiguity in what you say you will do (even if in reality you might change it later).