Write persuasively - you're selling a concept. You're not writing a term paper. Remember the reader, above all. Write so the reader, any reader, from any profession, can read your proposal. Simple, clear, concise sentences.
Writing is easy.
Never, ever cheat on margins, pages, words - on anything . When developing a budget, think project budget first. List every penny it will take to run the entire project. Then think, what part of this budget is appropriate to request from the funder. No grantmaker will fund every cent of a project.