Thick, hardback books works best to make this, but most books will work.
Step 1: Equipment
A book you no longer want
A pen knife or Stanley knife
Step 2: Step 1
Pick a page,30-40 pages away from the start of the book.
Draw 4 lines, parallel to the edges of the page, a few cm away from the edge of the book.
Step 3: Step 2
You may need to sharpen the knife every now and then, as paper dulls the blade.
Carry on cutting along these lines until you reach 30-40 pages before the end of the book.