This answer is from Isaac Stewart, our in-house art director, but I agree wholeheartedly.
Hire a Cover Designer/Artist. If the book looks professional, a reader is more likely to click on it.
Conversely, I believe that if you have enough drive and time, you can figure out book design for yourself, but like anything, your first attempts are probably going to be subpar. If you are as interested in book design as you are in writing, then by all means, take the years you need to figure out the trade. Then you can write books and design the covers and feel like an all-around awesome superperson.
But ideally, you want to be writing books, so almost universally I suggest that self-publishers hire a professional book designer. You want your book to grab the right audience and look professional. Too often, people try to do the cover themselves, using programs not meant to design covers. So they’ve hired a high school art student, or the neighbor’s artistic nephew–both of whom are great artists, probably, but they lack the experience and finesse of a professional. Same goes for typography. You really need to use the right tools for the job.
A designer is going to have access to the right tools and be able to help a self-publisher hit the market with a professional looking cover. A Google search will turn up ebook cover designers, but make sure their work looks professional before you hire them. If their work–or your own attempts–start looking like something from the Lousy Book Covers blog (http://lousybookcovers.com/), then you really ought to look into hiring someone else.