Editing is really the heart of the writing process. This is where you are able to clarify and tighten your narrative into a compelling proposal. A common saying among writers is that writing is rewriting. There is no good writing, only good re-writing. Great writers do this instinctively. For the rest of us, we need to practice.
Planning ahead will give you the opportunity to re-write. You must factor this stage of the writing process into your overall timeline. There is nothing like the luxury of time near the end of the grant writing process. You know all about Murphy's Law, my printer will certainly jam when I try to print Murphy's Laws. Very few of us have the ability to only write a grant; during this process we are keeping up with our daily work and home commitments. Time to rewrite is a luxury that you can afford with appropriate planning.
So my best piece of advice is to sleep on it. Wait two days to begin the editing process. Going at this with a clear mind will help you find what works and what doesn't work in your proposal. What seemed logical at the time of writing, will now stand out. As you begin to edit, remember that this is the time to cut, not add. Most of us are too wordy in our writing. Use this time to get to the heart of what you are trying to say. Sure you will need to add a word here and there, but for the most part you should be trying to be as concise as possible.
During my first take at a rewrite, I get ruthless with prepositional phrases. This is where I tend to be too wordy. Prepositional phrases tend to clutter my writing. William Zinsser, author of the classic guide to writing nonfiction, "On Writing Well" states that "clutter is the disease of American writing." Now in its twenty-fifth anniversary edition, Zinsser introduced me to the phrase "verbal camouflage." Zinsser can show you how to simplify and I encourage you to read his book. Some of his examples include showing us how a long word is often no better than a short word. Clutter is really the enemy. Why use "assistance" instead of help? Or why not try "many" instead of "numerous", or use "do" instead of "implement"? Zinsser teaches us to bracket parts of our writing that we can eliminate. You may need to bracket and remove an adverb that has the same meaning as a verb (for example, "smile happily"). You may need to bracket and remove an entire sentence. For example, a sentence that repeats what the previous sentence says or may include information that the reader doesn't really need to know or could figure out for themselves. Cutting and simplifying will give your writing an economy and tone that is sharp and focused. Show no mercy.
Your proposal will no doubt have been word processed, so take advantage of the spelling and grammar checking capabilities. Make sure that the finished copy and appearance have numbered pages, headings, and clean margins.
After you have simplified, spell-checked and generally cleaned up the final look, share the document with colleagues and ask for their insights and reactions. Particularly ask for their comments about clarity and content.