How People Buy Books
People are all over the place when it comes to what it is that makes them choose one book over another. As with all of publishing, it is subjective.
However, think about what you do when looking for a good book, whether you are in a bookstore, library or looking online. I'd bet it's a process and it's one that many people use.
Title and/or cover image attracts the eye and leads the prospective reader to pick it up.
Hardcover they read the inside flap to learn what the story is about and what it's like. Softcover they look at the back.
Table of Contents is next, especially if it's nonfiction. Sometimes people actually read a couple of blurbs, but they are looking for people they know they like saying they will like your book.
They skip the forward and other front matter to see if the first sentence pulls them in or not.
Then they go to the back to learn more about the author and what the author looks like.
Then they carry it around to look at other options.
If you think of marketing your book in the market as a series of steps outlined above, this will help you focus on the elements of the above and what you need to do to get it right.