Cover: Your cover needs to be on point, people browsing through Amazon won't notice your book unless you cover makes them.  You're competing with other books and you want your cover to be the one that makes people go, "Oh, what's that"

Description: 50% of sales are lost through your description.  Yes, you heard that right!  Some people want to know more about the book and will dive in to read what it's all about and if your description doesn't sell you've lost the sale.