I am going to use as an example the cover of a book I received a few days ago and it is killing me that I can't read it yet. I have other books I promised to look at first and a lot of other stuff on my plate just now. And it isn't just that I have enjoyed this author's previous work, it is this cover:
So, here the are, Emily's handy dandy 4 Qualities of Good POD Cover Art.
1) Good POD cover art looks like someone has spent a good long time getting the cover just right. If an author is particular about the cover art there is a good chance they made the effort to prepare their manuscript in a professional manner rather than running a first draft off with a stock cover and releasing it. Even if I don't like the art, there are points for effort.
2) Good POD cover art is pleasing in appearance. It uses a balanced composition, a clear font and an appropriate color palette. The image shown is not amateurish in that 'made by my cousin Bob who loves Poser' way. Any artwork or photographs used were created by someone with talent. Many people can write well but have no taste when it comes to visual arts--these people should get help with their covers!
3) Good POD cover art begs a question. You don't just look at and think 'okay, pretty.' You look at it and the art itself poses a question to which you immediately want to know the answer. This is a great general rule for any illustration, in good illustrations there is a feeling of a story going on right there in the picture. And don't tell me that a Japanese archer in antiquated dress with some kind of serious automatic weapon doesn't make you go "hmmmm".
4) Good POD cover art intrigues, but also suggests. You should have an immediate feeling about the potential content of the book. So far I am thinking slip stream, I am thinking Japan, I am thinking the potential of some kind of conflict... I am anticipating finding out how the prose will match the expectations set up by the cover.
In short, all I have seen so far is the cover and I've already been thinking about this book on and off for days. Now that's a cover.