How do you order the books on your shelves?
Umm. It's ... complicated. Or at least, multi-layered.
1st sorting layer: Genre / Topic
* Classics and LitFic
* Mysteries and Suspense (everything from Golden Age and classic noir to contemporary, including spy fiction, except for historical mysteries)
* Historical Fiction (including historical mysteries)
* Supernatural & Speculative Fiction (fantasy / sci-fi, supernatural, horror)
* Nonfiction: History and Biography
* Nonfiction: (Popular) Science
* Nonfiction: Law and Economy
* Nofiction: Philosphy
* Nonfiction: Dictionaries
* Nonfiction: Travel and Geography
* Nonfiction: Artist Biographies (classic rock and movies / theatre)
* Nonfiction: General / Other
* All things Los Angeles / Southern California
* All things cats
* Coffee table books
2d sorting layer: Language and Origin / Setting
* North America (USA and Canada)
* UK (with a separate "Scotland" shelf)
* France / French Literature
* Hispanic Literature (both European and Latin / South American)
* Portugal and Portuguese Literature (including Brazil)
* Scandinavia / Nordic Literature
* Eastern Europe
* Caribbean (English and French language; Hispanic Caribbean see above)
3d sorting layer, version (a): Alphabetical by Author
E.g., in the shelves for North American, Irish, Scottish, French, Hispanic, Portuguese, Italian, Eastern European, Russian, African, Caribbean and Asian literature; ditto some of the nonfiction shelves.
3d sorting layer, version (b): By Era / Topical Association
E.g., in the shelves for English and German literature (roughly, by historical era), nonfiction history (ditto) and most of the other nonfiction shelves, as well as all of my mystery, fantasy / sci-fi / supernatural / horror, and cookbook shelves (mystery: by sub-genre, e.g., British Golden Age, classic noir, etc.; speculative / supernatural fiction: by type (fantasy, etc.); cookbooks: by region and publisher).
This includes dedicated shelves for my favorite authors (e.g., Shakespeare, Agatha Christie, Dorothy L. Sayers, the Mann family, etc.).
Even without having entire dedicated shelves to themselves, books by the same author are kept together; series are generally in publication order.
3d sorting layer, version (c), as well as a sub-layer by expedience to all of the above: As shelf space allows!
The more frequently this occurs, the more it is obviously a sure fire indicator that the acquisition of more shelf space is becoming a matter of urgency. (Problem: There is only so much more shelf space that I can add -- read: not a whole lot.) Currently most prevalent on my "Scandinavian literature" and speculative fiction and supernatural shelves ... as well as on the dedicated Shakespeare shelves.
(The photos in this post are, incidentally, from the time of my major shelf reorganization a year ago. Since then, things have, alas, generally taken a ... decidedly less organized turn yet again.)