What message do you want to convey to the readers of your eBook? If you think about that you will know what you will have written in your book. If you begin with the end in mind, you will be constantly working toward the goal of delivering the content and information that you intended to on the day you first decided to write an ebook.
As you make notes for your outline picture your reader reading the last page of your ebook. What will they now know that they did not know when they began reading on page one of your ebook? Think about the books you have read. What did you hope to find out or learn by reading them? Your reader will also have an idea of what they want to get out of your book. Begin with the end in mind and your ebook will have great value to all who read it.