How To Include A Link To Your Next eBook
On the first blank page at the end of your eBook, put a highly visible link to the webpage where they can buy your next book (or books). e.g. link to each book’s Amazon page. You’ll also want to include a decent sized picture of the book cover in each case, as this will act as a highly persuasive promotional billboard.
It doesn't get much simpler than this, does it?