For fixing single pages that have come used, rather than using paper strips as Helen suggests it can be better to just glue the page in. That¡s especially true if there are lots of loose pages, so that they bulk up and can cause a bulge on the spine. And glued stripsof paper have a tendency to deteriorate in time abd come away.

Here's a video showing how it’s done. https://youtu.be/xvTK8tUCcmA.

There's a comment below tge video which goes to the heart of what I said in my earlier post about the quality I value that seems to go with the craft: "it's easy to mess something up if you're not doing it slow, calm and steady."   A motto to live by…