Submit all and only the materials the publisher asks for. See Manuscript Format below. A proposal can vary from a detailed synopsis to a query letter with synopsis and partial. Find out what the publisher means by the term. Follow Other Submission Guidelines.
Publishers usually state other submission requirements in their guidelines, tip sheets and listings.
Even for those that do, it is considered very bad etiquette to send a multiple submission without stating clearly in the cover letter that the manuscript is being considered by other publishing houses. If you're serious about being published, it pays to take the time to submit a professional looking manuscript. Your manuscript should be typewritten or letter-quality printed. Use black ink only. This leaves room for an editor to pencil in comments.