You don't know just how make-or-break this can be.
Let's take for example The Casual Vacancy, since I just read it and it is a perfect example of what I am talking about. Milk your book cover for ALL it can give you. And here is the kicker/secret:
Your book cover can mask major 'faults' in your book.
The Casual Vacancy was incredibly grim, morbid, and depressing. If I had to read it without the jacket copy (I can't believe I'm saying this) but I bet I would have been much, much more depressed by the book than I was. The reason I wasn't was because of this beautiful little deceptive angel:
That book cover is NOT morbid.
That book cover is NOT depressing.
In fact, it is downright happy and cheerful.
Thus, I read, expecting something not depressing, not morbid, not cruel. And, thus, I found things that were happy and cheerful.
Here is a little method to cheat your way out of your book's one-major-unworkable-mood-related flaw, if you so please. Say you are writing a tragedy, or a very, VERY depressing book (I am). If your book cover is light and colorful, it will balance out the possible negative effects of the book's sadness. Now, this happened to me for sure with The Casual Vacancy, and I suspect it happened to many other people, but don't take it as a hard-and-fast rule.
This is NOT to say that you can write the most morbid, depressing, frustrating book in the world, and expect the book cover to make it uplifting.
The book cover only gives the book the small push it needs to get the message closer to the author's intention.
Say you've written a Bella Swam protagonist who has that bit of courage inside her, but you are afraid the reader won't understand it; make the cover display the heroine as a strong lady, and the reader will pick up on all her (possibly, small) displays of strength.
It is the ultimate trick, the ultimate technique. (I resist saying 'cheat' because I do not think it is a cheat at all -- only a method to point the book towards its true direction.)
Again, the cover only gives the book the push it needs to get the message closer to the author's intention.
This is a beautiful, BEAUTIFUL technique to give your book the push it needs.
If you are afraid your book's message will be taken in the wrong direction, make the cover opposite to the supposed theme, and closer to your intention.
If the reader comes to the book with expectations, if he/she comes to the book looking for something, he/she will find it.
This is what makes the book cover a work of art; this is what gives it, truly, a life of its own, complementing the life of the book. This is what makes it the ultimate book cover -- when it complements and helps the book and author.
Happy book covering :)
Should the words stand on their own merit, or can the author rightfully bend the packaging to make the product (the book) more appealing? Is this deceptive?