Napoleon Hill talked about mastermind groups more than seventy years ago, after having heard about them from Andrew Carnegie many years before that. Simply put, a mastermind is a group of like minded individuals who meet regularly to discuss ideas, strategies and plans to achieve their goals. They are usually from different walks of life or professions, but you can do whatever works for you.
The ideal mastermind for someone writing an ebook would include people who had already written and published a book, traditional or ebook, and someone who had marketed products or services using the internet. Find several people who you respect and form a group that will meet weekly. Make sure that each person gets something from being in the group or there will be no reason for them to stay. Allow them to read your material and ask them for suggestions and feedback. Look for successful, positive people who are excited at the prospect of exchanging ideas with you.