Jot down a list of emotions and ideas that your book brings up when you read it. List its central themes, settings and characters. Write down the images these lists invoke. Choose several of these images to consider incorporating into your cover.
Search through commercial stock photography and art websites for images for your cover. Rates vary according to agency. For example, some images are royalty-free while others may cost $100 or more. Typically, once you pay for your selected photo or art, the website will allow you to download a high-resolution image. Make sure the resolution is at least 300 to 600 dpi.
Select photos or artwork you already own or borrow an image created by a friend or acquaintance if you're working with a limited budget. Make sure you both sign a short agreement that outlines how the image will be used and whether she will receive any compensation or other consideration in exchange for the right to use her image.
Obtain the book's final dimensions from your publisher or printer. Commercial paperbacks are often 5 1/2 by 8 inches or 6 by 9 inches, but your publisher may have another size in mind. Also ask how wide the spine will be, as you'll need to allow enough room when designing the cover to accommodate the title and your name on the spine.
Design your cover in a program such as InDesign or Quark, or hire a designer to lay out your images and text to your specifications. The cover should be designed so that it is one landscape page, with the back cover on the left, the spine in the middle and the front page on the right. Leave at least a .125-inch bleed on all four sides of the document, so that your images and text are not cut off in the final printout. Use a large, readable font to make sure the title and author name stand out on the front cover. Your title and name should also be legible on the spine.
Drop in your back cover text (a catchy summary of the book, along with any advance praise it has received from reviewers or fellow authors) into the design document. Your publisher may also request a barcode in the lower right-hand corner of the back cover. You can easily create this by using one of many free online barcode generators that produce barcodes as jpg or png files. Ask your publisher whether you should include just the price in the barcode, or whether you'll also need to include your name and the book's title.
Save your Quark or InDesign file as a PDF. Your publisher may have additional requirements. For instance, you may have to send the publisher your Quark or InDesign file as well as your fonts and images on a CD-ROM, so be sure to ask before submitting your file(s) to the company.