Source: EContent Magazine
As this excellent article points out, creating a premium version of your book is a great way to generate more profit with little effort.
From the original article:
“If you’ve published a digital book designed for e-readers such as Kindle, you should consider taking that same content and publishing it with additional media as a premium version, at a premium price, for users willing to pay more for more content.”
While the article focuses more on non-fiction books, the same tips can easily be applied to fiction books, as well. As this article points out, just adding something extra that you can do yourself (such as a video) will get your more devoted fans to buy a special edition of your book at a higher cost.