In this article, we discuss how to write a business proposal letter and we offer sample letters and templates you can use as a guide. These templates are suggested forms only.If you're using a form as a contract, or to gather personal (or personal health) info, or. A business proposal typically has two parts: Cover letter; Proposal document. A shorter proposal may combine these two parts into a six to eight page document. Writing a business proposal might sound intimidating, but it's not as difficult as you might expect. Click here to learn what to include and how to write. Doing Business with the City. Step 1: Fill out the form. In this article, we explain how to write a business proposal letter and examine a few sample letters.