When I was waiting for an author signing at ALA I was next to the Bloomsbury publisher booth. Myself and one of their publicists started talking about the process of making a book cover, and it was super interesting! She got me in touch with someone who makes covers and I did an interview with her. If you want to know how publishers creates covers like Wild Cards, Crown of Midnight, and Me, Him, Them, and it, check out the interview!
and then we go from there. For some books, I have done more than 50 drafts. For others, one of the first three to five drafts will satisfy everyone and we just fine-tune it.