A proposal is a sales document, not an informational document. Include the necessary information, but make it persuasive.
Reacting to RFPs doesn’t work. If you don’t have a relationship with the client before the RFP is issued, it is unlikely you are going to win.
If you add just one more comma at the end of a list, you will make your writing clearer.
You should always include a cover letter when you send a proposal. It’s good business etiquette, it’s polite, and there’s no reason not to.