Connie Willis, Lincoln's Dreams
Jacques Bonnet devotes a chapter to organizing books in Phantoms of the Bookshelves. He credits Georges Perec with this list of the various ways one might classify books:
by continent or country
by date of acquisition
by date of publication
by literary period
by frequency of consultation
Often we may use two or more of those systems at the same time. For example, those old science fiction books of mine, which at one time were shelved in order of acquisition, are now arranged alphabetically by author. Most of my novels are arranged alphabetically, but I also keep mass market paperback novels apart from the novels in hardback or trade paperback editions. Some unusually large works of fiction, such as an annotated collection of Ring Lardner's baseball stories and a copy of The Wizard of Oz illustrated by Michael Hague, are kept on a shelf with mostly nonfiction books of large size. Few of my bookshelves are large enough to hold big books, so I don't want to waste that space on books of ordinary size.
As for most of my nonfiction, I have separate areas for history, natural history, religion, show business, sports and so forth. It helps me to find what I am looking for, at least most of the time.
Organizing my books has become more challenging as I have run out of shelf space and been forced to just pile books on the floor of my attic library. Yet I attempt to keep these piles somewhat organized, unread books in this pile, for example, and those I've read in that one. The novels in stacks are still organized by the names of their authors. There is an M stack and an R stack and so on.
Bonnet has a telling phrase in another chapter of his book: "they are classified somewhere in my mind, as they are in my library." I see this in reference to the Willis character, Broun. He claims to know where all his books are despite their apparent lack of organization. In the same way, I resist my wife's offers to organize my desk, fearful I may not be able to find anything ever again. Perhaps it is really in our minds, not on our shelves, where collections of books turn into libraries.