Everything I've read regarding choosing a cover has been helpful. You want something that is going to look good both as a thumbnail image (for ebooks) and on a paperback, if you're going that route as well. I am. I plan to publish both as an ebook and in a paperback form.
But how to choose? I've been looking at other novels to see what sells, and then I've gone through photographs I have taken, or friends have done.
I've gone through different stock photo websites. Looking for something I want to purchase the right to use. I've enlisted the help of a friend of mine, who is a graphics designer to help me out. We'll see what he says. Above, are just a few of the mockups I've tried. I've still got time and should probably get back to editing, but this keeps me reminded I am moving forward. This is really happening.
You might not be able to tell a book by it's cover, but it certainly can't hurt to have the right one.