Having seen the covers of my own novels, it's become clear to me that most publishers have no idea what package elements attract readers. So, for what it's worth, here's my own idiosyncratic analysis of what makes a book jump off the store shelf and into my hands. The first thing I look at is author names .
Unknown authors get more consideration if the publisher has prominently positioned their names.
Next I look at cover art . I'm an SF reader, not a fantasy reader. Anything that looks like a fantasy is immediately eliminated from my consideration. Also, if I recognize the cover from advertising in Locus or SF Chronicle or elsewhere, I'm more likely to give the book some attention. After that, I look for any indication that this is a book in a series.