The name of the author and title of the book should appear clearly on your book cover. By adding the proper colors and types to symbolize the subject of your book, you will get to know your potential readers about other projects. This is a great mockup featuring three books. That said, you have enough space for showcasing different stuff without a hitch.
As you can see, the books are standing on a flat surface. In this case, you can add your designs through the cover of the book as well as the spines of the three books. Needless to say, you can add different colors to the books or keep things simplistic by adding one color.