By subject

Well. This system gives almost endless opportunities – and endless difficulties. First you would have to decide: which subjects? This would of course depend upon your selection of books. For example, some people could fill shelves with novels about fish, or swords, or sculpting, or cars, or pyramids, or theatres, or ghosts, or baking. Others would need to divide their novels about vampires in Louisiana into subcategories. But even when you've gotten that far, the work is far from done. Because a couple of your novels about fish will also be about sculpting, and some of your books that have a lot of good things to say about cars will also have a point or two about pyramids. To be quite thorough, you will need to make a catalogue, fully cross-referenced. And, obviously, lables for the shelves. But little things like that have never stopped you before, have they?