I can't even express enough how important it is to have an eye-catching book cover.  It's literally the first thing readers see along with the title. It is also important the book cover have that connection with the story. For example, if your book is about vampires, you don't want a book cover with a bowl of fruit or a bunch of balloons. Try and connect the book cover with the story.
Also, I know this is going to come off nit- picking, but readers also pay attention to the font. Make sure readers can see the title on the cover. 

The book cover, title, then the blurb are the three things we look at before deciding to read the book. They all need to catch our attention.