The fifth and final part of a book proposal is the Sample Chapters. Normally two or three are included in a book proposal. These are double-spaced and should reflect the quality and substance of your book. I suggest sending the first two or three chapters to give the editor a sense of continuity. Some authors prefer to send the first, middle, and last chapters; others prefer to include a chapter with specific significance. You be the judge regarding what is best for your manuscript. The chapters should be double-spaced.
It is important to keep your entire proposal under 40 pages. When an editor or agent first looks at your manuscript, he or she will probably only give it about 20 minutes. If it is too long, the editor will not be able to get a good overview in a short time.
Different publishing houses and agents have different requirements for writing a proposal. What I have given you here will be required by most of them, but they may also require additional material. Be sure to check the proposal guidelines for the publishing house to which you wish to send your book proposal before completing it.
I think writing the proposal is the hardest part of writing an entire book, but a good proposal is your ticket to receiving a contract.