The proposal is a critical piece of the sales process, but it’s not a goal in and of itself. Sometimes, though, we get wrapped up in things like “how many proposals did we send out this week?” If you’re getting a lot of pushback on your proposals, you may be presenting too early.
Check out Marc Wayshak’s piece: Three Signs Your Presenting Too Soon, to see if any of this applies to you. (Marc focuses on presentations, which is not quite the same things as proposals, but the concepts still apply.)
I’d add a fourth: staring at your screen, unsure of what to write. This is often because you don’t know basic things about your customer’s buying process and solution requirements. Just ask.