Proofread carefully for typography and spelling. Sloppy typesetting and spelling conveys disrespect for the selection process, and is insulting to the reviewer. Finally, always remember that, due to the cut-throat nature of the US funding system, the US competition is generally much more experienced in proposal writing and overall salesmanship. There were some proposals which failed to get time mostly because no one on the panel knew enough to be able to put the specific target in the bigger context, and the proposal failed to make this clear. When writing a proposal the authors should assume that at least some of the Panel Members are not experts in the particular field.
Style is as important as is content in getting one's proposal approved.
In a number of cases it was clear that the basic scientific idea was interesting but not all the details had been sufficiently worked out in order to demonstrate that the proposed observations were outstanding. In summary, people should be aware that at this level of oversubscription only outstanding proposal have a chance, and not only the idea has to be excellent but also it has to be described in a synthetic but effective way. Fully polished English is not required, but obvious typos, missing references and the like do not read well. Therefore, it is important to make the proposal attractive also to people slightly outside your own speciality and give the referees a chance of understanding the crucial points. A well written introduction is therefore essential.