This is echoed from the #YourNextFavoriteAuthor blog post Here. (June 29, 2016)
Since I’m both a reader and an author, I look for a cover that integrates the necessary text into the cover art.
For the artwork, I look for pieces that I’m interested in – things that tell me what genre the book is, what era the book is set in, and hint at the premise of the story. I’m picky about covers that depict actual scenes in the story – too many times those wind up being spoilers on the second (or later read through) which can reduce my desire to re-read a good book.
For the required text I prefer not to hunt through the cover to find the title and author’s name. If it’s part of a series – that can be buried for me on the front, but it is handy to have the series number on the spine. The big exception to this, is if the individual book titles in the series make sense when they are strung together as a sentence. (I’ve seen that done a couple of times. Love it!)