eHarlequin, as part of their editorial week have a great podcast on this topic.
They talk about giving readers what they want and what they didn't know they wanted. This is the combination of a story of your book and a book to sell, which uses the themes and hooks of popular stories, but giving them your unique voice and twist.
It really is about how to stand out from the crowd and selling your book, and still writing the book of your heart.
Well worth a listen!