Read the rules and save yourself a lot of irritation later. This one ought to be obvious, but we create an incredible number of misspelled documents. Remember that reviewers tend to correlate bad spelling with bad science. Have someone you trust review your proposal for clarity. The harder a reviewer has to work to understand your proposal, the more annoyed they get.
Annoyance is bad.
This means to place your work in the larger context of your field. It is an interesting fact of astronomy that all great astronomers do NOT come from your school, do NOT think your field is the grandest thing since the invention of fire, and maybe even do NOT think that you are the best scientist since Archimedes. Reviewers are annoyed when they need to use a magnifying glass. Clearly state the scientific problem. Credit other people in the field where appropriate.