It is a good idea to write a book proposal for your ebook, even if you never plan to take it to a publisher, a literary agent, or self-publish it. The reason for this is that writing the proposal will make your ebook more clear in your mind and you will have an outline to guide you.
You book proposal should include what your ebook is about, who your target audience is, how you intend to market it, and what other books have already been written on the subject. It will also discuss how your book will be different from the others (your USP or unique selling proposition) and an outline of your chapters. This way you will have mapped out a plan to get your ebook written and ready to move on to the marketing and selling. If you eventually decide to publish it through traditional channels, you will have your proposal ready to present to a publisher.