I organized left to right from the bottom up. I knew bottom-to-top was a bass ackwards configuration, but when I moved my books to one large, tall bookshelf, I had to start at the bottom so that if I left any shelves empty, they would be at the top, in order to prevent the shelf from being too top-heavy. Many of my heaviest books were non-fiction, so I put the non-fiction at the bottom. Non-fiction was organized by subject matter in relation to each other, instead of alphabetically. For example: my music books were organized by song books, then organized by instruction manuals, then by music teaching books. Next to those books I put general teaching books, then childhood psychology books, then philosophy, and progressed upwards to human evolution, and then human prehistory, human history, and historical fiction, all organized by time periods (oldest to most recent, left-to-right). To the left of those books, I placed the legends and mythology, organized by mythological time periods. Next to those I put fantasy, at which point I stopped organizing by time periods and started organizing alphabetically. I organized the rest of my fiction alphabetically and in broad sections.