My own background in art and design may actually hurt me when it comes to creating book covers. I’m not inclined to be satisfied with the all-the-same approach that is so often seen and even advocated for genre fiction. The argument is made that YOUR cover should look like other covers in your genre to guide those poor not-so-bright book buyers. As if they couldn’t read the description!
I do prefer the more abstract sort of approach one may see with mainstream/literary fiction. Not that it shouldn’t relate in some way to the subject matter but we don’t need another generic girl with a sword to sell our fantasy novel.
My top priority in this day of online book sales is that the thumbnail be quite clear and understandable, with title and author large enough to be read. Many typical covers become indecipherable when reduced in size. This is another argument in favor of a more abstract approach, with bold, simple designs. Some number of my covers are essentially done as silhouettes, black on solid color, with title and author name as large as I can get away with.
I recognize that no one is going to walk into a bookstore and buy one of my books by its cover. It’s all online and that simply calls for a different approach. How it looks at Amazon or on the publisher’s website is what matters. And we must keep in mind that the material WITH the cover is as (if not more) important than the cover. A good blurb, the right keywords — that is what we need. Readers want words, after all.
Until fairly recently in history, book covers had no pictures at all. That practice sort of slipped over from the magazine business and was, perhaps, influenced as well by movie posters. When racks of paperbacks became ubiquitous, so did the cover illustration, and it is just as important now on the internet. Yes, a cover does need to attract attention, still. And maybe looking like every other cover is not the way to achieve that.