While I was researching the design, I trawled through the dusty remainder bins of the internet and what I found indicates a disconnect between the burgeoning independent book industry... and its cover.
I spent years working in bookstores, watching patrons peruse the shelves, picking up book after book and putting it back without so much as glancing at the jacket copy. What were they looking at? Title? Cover art? What was it about the books they put back that didn't appeal to them?
I posit that in many of those cases it was the cover. Something about the cover got in the way of them opening the book and reading the words.
I admit the possibility of bias, but I've watched it happen too often to discount it. Publishers agree with me.
In fact, in "ye olde days" (which was actually about six years ago) the best thing a publisher could do to get a book in a customer's hands was to make a deal with a bookstore to put it on a table, an endcap, or on the shelf with the cover facing out. This is called a "Co-op" and it's been the way of things for decades in both the book and music businesses. Heck, they do it in grocery stores too.
Why does it work? Because publishers know that a decent cover can get you to pick up a book. And if you pick it up, you're significantly more likely to form a bond with it, and ultimately buy it. 
Here in the future (cue beepy futuristic Star Trek noises) where we buy most of our books online, all book covers get the full-face treatment (which is awesome) but they're shown the size of your thumb print (which is not).
On the screen of the laptop I'm using to type this, Amazon displays thumbnails at about 100 pixels by 140 pixels, or approximately 1/3 inch wide by about a half inch tall.
That's about this big:
Consumers do indeed judge a book by its cover. Is it logical or fair? No. Does it happen? Constantly. Do I judge a book by its cover? No, but I do judge publishers by them. . . or rather I take it as a measure of their faith and how devoted they are to marketing the book.
As both a reader and as a designer, the cover art tells me how seriously the publisher takes the book. It tells me that they invested the time, energy, and money in getting a designer and a book packager in a room together to give the book a visual identity and that ineffable thing we used to call "shelf presence" but I suppose we should start calling "thumbnail presence" that gets people to pick it up and give the words a chance to seal the deal.
At best, a book cover will make the buyer click on it (or pick it up) but really the best you can hope for in the thumbnail age is for it not to get in the way.
The fake cover shown above is frankly a bit pedestrian, but it works. It's imperfect to say the least, but it's still perfectly adequate cover for a science fiction book about melty buildings. I cobbled it together from a picture my wife took of the Experience Music Project which, frankly, looks a bit like Tupperware that melted in the dishwasher. (I felt bad doing this to a perfectly good photo. Behold the majesty of my lens flares!)
If nothing else, it proves that you don't have to be Saul Bass to make a workable book cover or poster. This isn't great, but it wouldn't hurt your book sales. Even with all the stops pulled, it still works as a cover.
Why? Because it adheres to some basics of proportion and composition (more on that in a minute). It uses a clean font that has been optimized for contrast with its background. There is nothing about this image that would make you skip clicking on it.
Let's look at a different picture that gathers together many of the most frequent cover design errors that I see as I trawl through Amazon's lists:
This is illegible. I see it all the time and it doesn't work on any level. A loopy handwriting font is bad enough, but it's in a color that isn't a sufficient contrast to the underlying image -- even in white against a black background as with the author's name you can't read it.
Note that this one barely works at a larger image size or higher resolution. Even blown-up, the red subtitle is gone.
Sometimes it's easy to see why one things works and the other doesn't. Even with all the silly Photoshoppery, When the Buildings Melt "works" not because it's brilliantly executed -- it isn't -- but on simplicity alone. Just being legibile will get you a long way. The curly font murders Swear Not by the Moon in its bed before we ever get to the contrast and composition problems.
This isn't my best work, but it is a bit better. At least you can read it.
The tapes and off-kilter type is very much a trend right now and it does look funky and youthful (I'm imagining this is a YA book). The font could be even clearer but I don't want to spend a lot of time on an example piece.
Note that I de-emphasized the author on this version just to make a point. Despite what our egos tell us, the least important part of a cover is the author's name. If you're not James Patterson or Steven King, your name isn't the prime selling point. It's a choice that not many are willing to take.
These aren't even extreme examples. Go through the lists of e-books uploaded by hopeful authors at any book site you care to name. You'll see every one of these problems and more that I haven't thought of.
The aesthetics of design are the work of a college degree and several library's worth of books. Which is to say that they cannot be adequately encapsulated in a single blog post. So why bring it up at all? Because it's the place where so many small publishers and self-publishers fall short.
Book selling used to be all about getting booksellers to lay your book flat on a table or turned face out on a shelf. Give the book prominence of placement and the chance for the cover to work its wiles and you're halfway to a sale. These days, it's all about clickable thumbnails.
A very basic understanding of graphic design is mandatory in that marketplace, but independent authors and small publishers the world over fail to fully appreciate the power of a thumbnail. If you don't believe me, go through the lists at your favorite online bookstore and pay attention to how many thumbnails are completely indiscernible.
Scott's First Rule of Design: "Possessing a copy of Photoshop does not make you a graphic designer any more than owning a stove makes me a chef."
I may be a foodie, I may even be an excellent cook, but it takes years of training, tasting, and all around hard work to become a chef. The best I can hope for is to be an enthusiastic amateur. And that's fine, but it doesn't mean I should open a restaurant. Technique is the product of training, taste is the product of training combined with experience. You cannot claim the funny hat without liberal helpings of both.
What you're going to turn out will be amateur work. That's okay. Make it the best amateur work you can. Honestly, you're ahead of the pack if your cover just doesn't actually deter sales.
Here are some very basic rules and/or guidelines:
- Don't use Microsoft Word or Paint: MS Word & Paint are not adequate to the task. Your image will bust into pixels as you re-size it and you will be sad. Happily, you don't need the full Adobe Creative Suite. Photoshop "Elements" contains all the tools you're likely to need and only costs about $80.00. This is a business you're engaged in. Invest in your business.
- Pixelation is bad. Work large and shrink it, don't work small and try to blow it up. While you're working, constantly apraise your image at every size it's likely to be viewed at. At art school, we were taught to think of every image as a postage stamp.
- Use clear, strong, fonts in colors that contrast with their background. Keep it simple. Ornate fonts are your enemy and have to be applied very carefully if at all. If I can't read your title, the odds of me reading your book are diminished.
- Learn the "Rule of Thirds" and stick to it. The Rule of Thirds is a quick way to attaining a decent level of composition and after awhile it becomes second nature -- without meaning to, I adhered to it even in the Swear Not By the Moon cover I posted above. The Wikipedia article on this topic really is pretty good. Click the link. Even professional designers and photographers only break the rule of thirds on purpose.
- You do not have to use a photo. I see so may photos on book covers that I feel like someone, somewhere thinks it's a rule. It's not. Also, as we've seen, photos can complicate the legibility of your text. If you do want to use a photo, use your own if you can. Take the picture in the best possible lighting and at the largest format your camera allows. Do not use a flash. Most bad digital photos can be made better simply by turning off the flash.
If you feel you need to use someone else's photo, you need to familiarize yourself with licensing a fair use. CreativeCommons.org is an excellent resource. I urge you to use a photo that is in the Public Domain (the Library of Congress or Wikimedia Commons are excellent sources) or a Creative Commons image that the photographer licensed for commercial use. If you don't, the image owner has every right to sue you.
- Fonts belong to their designers. The same rules of photo and image licensing apply to fonts. When you choose a font, you must be sure you have permission to use it commercially. There are a lot of free fonts available. Shop around. (Once again, the Creative Commons folks can help you out there. See above.)
- The Three C's" Contrast, Clarity, and Composition. These are the three concerns you must always keep in mind as you're choosing every element of your design. As in storytelling, the parts are in service to the whole, not the other way around. I don't care how much you love the photo of the kids playing in the mud puddle, if it doesn't work, chuck it.
- Go to a book store or a website that sells books and LOOK at the covers. Take note of what makes you want to click to see more and what doesn't. Go thou and do likewise.