Some people are just not cut out to be proposal writers. Often technical staff don’t have the background or training required. However, you can usually coach them through it and get usable content from them. Sometimes they even turn out to be quite good. But every once in a while you meet someone who you think gets it, but every time they go back to their office and write something, they fall back on old habits and turn in something that has to be completely rewritten.
Normal approaches aren’t going to help you with these people. Don’t even think about giving them a style guide. They don’t need training, they need practice. And lots of it, over an extended period of time. Which of course, with a proposal due, you don’t have the time for.
The only thing you can do is cheat. Or more specifically, give them a cheat sheet. It’s got to be short, no more than a page or two. And it’s got to provide direction that is crystal clear — not the normal chapter on how to be an effective writer. Don’t even try to explain win strategies and themes. If you want to dramatically improve what you get from them, you need to focus all of your efforts on changing how they think about writing. You’ll never reach them by focusing on the mechanics. Instead, get them to think like a proposal evaluator and give them a few simple instructions they can follow like these