The most important factor concerning paper for a book is that the grain of the paper runs parallel with the binding edge of the book.  Click here to see a short video explaining paper grain and how to determine which direction it runs.

Another important factor to consider is margin size.  1/2" to 3/4" is required on the inner margin for sewing and an additional 1/2" on the outer edges will allow ample room for trimming.

We can bind books from single sheets, or from folded signatures.  Books with folded signatures generally lay open better than those bound with single sheets, but there is a trade off, as the expense in both printing and binding in signature form is greater.