Measure the book's spine so you buy the right size tape. You'll need dimensions for the length as well as the width. Buy tape that is 1 inch wider than the spine and thick enough to hold the pages of the book.
Open the book so the front cover and first page are touching. Apply a piece of tape to the center, and smooth it down. Repeat this for the back of the book.
Cut a piece of tape for the spine of the book. If you're fixing a paperback, it will be the same length; if it's a hardcover, make the tape slightly longer than the spine.
Hold the book so the spine is facing you, place the tape over the spine and smooth out any air bubbles. For hardcover books, wrap the tape around the spine's edge; cut off any excess for paperbacks if needed.