Or, Why You Keep Hearing "Make Your Name Bigger!"
If you studied movie poster composition and layout, you'd find that almost all good, eye-catching designs fall into a very few broad layout categories.** If you hadn't (like most of us), take the cliff-notes version and go read this class handout (PDF format) so we're all on the same (cover) page. http://eetwagga.riverinainstitute.wikispaces.net/file/view/Poster+Composition.pdf
OK, now for ebook cover design, we're going to focus on two layouts. They call them "The Z Layout" and "Perspectives Layout" in that handout, but I'm going to use the terms I was taught instead: The Hourglass, and The Triangle.
Why "The Hourglass" instead of "The Z"? Well, because it's much easier for me to look at a cover, draw an X across it, and see what size font and image makes the whole thing feel balanced - the further away from the focal point, the larger the font needs to be. (Also, because I learned that term first.)
StarDogs note the starship is not at the exact center of the page, but if you draw an X across the cover, starting at each corner, the starship fits almost completely inside the hourglass. Thus, it feels balanced to the eye. The tag line, on the other hand, does not - and that's why it looks slightly "off" for the cover.
Ride The Rising Tide On this one, the starship itself is positioned to outline the X, and completely fills the hourglass. Because the title is so long, it's unbalanced for an hourglass, and the tiny series heading would have been too short - unbalanced - if stuck beneath the title. So, Oleg put it on top, making a second triangle of the series/title text.
In case you hadn't figured it out, you're rarely going to get a "perfect" design illustration that absolutely follows the outline of the hourglass. It's a rule of thumb, not a commandment, and it's supposed to help you figure out what looks subconsciously pleasing to the eye. You can violate the heck out of it and have an awesome cover - but it really helps to know the rules so you know when and why to break 'em.
Baptism By Fire here, which is a great book in the Monster Hunter International style, has a good strong central image, and the top text is perfectly balanced for the hourglass layout - but the Author Name at the bottom is way too small. To properly balance, it should fill the bottom of the image in the same way the title fills the top. This is (a large part of) why we keep saying "Make your name bigger!"
Ok, on to The Triangle, which had a much more complicated name of "perspectives" in the handout. Every Perspective has a vanishing point and a foreground making a triangle. It's much simpler to just say "triangle" instead of trying to isolate the vanishing point, because really, the triangle's the thing wherein we'll catch the conscience of the king... or at least the pocketbook of the reader.
Awake in the Night Land is an easy start - it's a great bloody triangle. Pointed up, as opposed to the usual pointing down, but easy to see. Again, like ride the Rising Tide, you see the long title made into its own little triangle, even as the central triangle of image grounds it point in the title.
- the triangle is in the bullet holes, with the point at the bottom right corner of the cover. Yes, he doesn't have a "title block" at the bottom, and it works just great. remember, layout rules of thumb to help make something pleasing, not ironclad laws.
Murder World: Kaiju Dawn did something really cool here, and it's the reason they're not going to get "make your name bigger!" - if you look at the monster head image, it's an offset triangle with the point grounded in the "U" of "Murder". The author names at the top are small - but they have subtle white steaks filling out the rest of the triangle, so they still look very balanced. Cool cover, guys.
I could go on and on, but hopefully this is enough for you to start looking around the top books in your genre and start seeing the layout and composition principles at work. A few final related points follow.
1. Make your name bigger because your author name is your brand. As surely as Nike and Pepsi want you to be able to tell their products at a glance, you want readers to be able to identify you in a 60 x 100 pixel cover image in some other book's also-bought or a search results page.
2. Make your name bigger because trad pub has trained readers that big names are important, awesome authors that should be bestsellers, while small names are forgettable midlist. You want to be a bestseller someday - start faking it til you make it, because the reader won't believe it if you don't design your cover like it.
3. When looking for good cover design for your genre, it's often better to check the top 100 print books in your subgenre than the kindle - because kindle has so many more authors who succeed despite their covers, or are in there for one day due to a bookbub promotion and fall right back out. Take what you learn about your genre and subgenre, and apply it promptly to your ebook and print book.
4. Typography is a whole 'nother can of worms, that'll take it's own long post, as is "cover art for genre/subgenre". This is not comprehensive, it's just an attempt to cover one portion of what makes a good cover.
5. When doing triangles instead of hourglass, they can absolutely be offset any way you want them to - but usually, they will face the bottom right (see Bad Penny, above). If there are people, they should be looking to the right, or to the bottom right. (If not directly at the reader/directly away from the reader.) The reason for this is very subtle - on english books, we read left to right, top to bottom. Grounding the image/action/attention to the bottom right automatically cues the reader to open the book / turn the page, just like when they reach the bottom right when reading on the text of a page.
**Oleg, please forgive the butchery of design principles about to be committed in the name of making the concepts understandable to authors.