Open a graphic design program. Adobe Photoshop, Illustrator or InDesign are all excellent software programs for creating e-Book covers.
Open a new document and format it to the specs of the e-Book; most e-Books are formatted in 8 1/2 by 11 inches. If the cover will eventually be used for print then it must be formatted in CMYK (cayenne, magenta, yellow, black) color format with at least 300 DPI (dots per square inch.) If the book will only be used for online purposes, then RGB color format and 72 DPI will suffice.
Sketch out some designs on paper with a pencil. Do a rough layout of how the book cover will eventually appear. Look at other e-Book covers and see what positive attributes could be applied to your e-Book. The title and author's name are the only required text. However, a brief description or tag line may be a nice touch. Let your imagination run wild -- and once a design has been chosen -- it can then be created in the graphic design software.
Use the tools in the graphic design program to create the cover. Remember that if images are used they must not be under a copyright. Using an image found online in an e-Book's cover may be copyright infringement. There are many royalty-free clip art and stock image sites.