Choose a piece of paper that you want to use to cover your book. Wrapping paper, the Sunday comics or just plain brown paper will do.
Place your paper on a flat surface. Open the book from the center and place it on top of the cover material. Cut around the perimeter of the book leaving a 2-inch border.
Remove the scraps from your work area and keep the book centered on the paper. Draw a line to mark the top of the book then another to mark the bottom. Remove the book and fold the paper along the lines you created. Put the book back and mark both sides then fold them the same way you did the top and bottom. This procedure creates pockets for the front and back covers.
Insert the front cover into the left pocket and repeat the process with the right side, adjusting the cover to fit over the book as you go. Reinforce your folds with glue -- be careful to glue the paper to itself and not the book.