How to tidy up a book case:
Insert yourself, butt first, into the shelf, so that you sit on the innermost row of books. Push on the front row of books with your paws. When you have pushed them far enough out, you can move down and use your body to push them all the way down from the shelf. It is more fun if you take many books with one push, but sometimes it is hard to do. Then you can take one book at a time. Make sure to see they fall all the way to the floor.