but in general, i arrange them by size and/or author depending on the shelf. so, i won't break up the WoT series for example, but if i have quite a few large books (and i do mean *large* ) they typically will go together whether they make sense together or not.

as an example of what i mean, on my one bookshelf i have right now i have on one shelf the following:
- total football (encompassing some 2000+ pages of the history of the NFL)
- the tao of jeet kune do
- ken kesey's jail journal
- various calvin & hobbes and bloom county anthologies
- the collected works of shakespeare (in a single volume)
- the collected works of eudora welty
- the collected works of langston hughes
- douglas adams compilation of the two dirk gently books (in one volume)
- schroedinger's cat and the illuminatus! trilogy (showing an example of not breaking up the author's works)
- isaac asimov "robots and empire"
- introduction to "the art of film"
- complete poems of t.s. eliot
- complete poems of william blake
- ulysses, and a combo book of "portrait of the artist as a young man" and "dubliners" again showing the example of not breaking up an artist's works.

the only thing these books all have in common is that they are roughly the same height with respect to each other, although they do reduce in size from left to right (or top to bottom of this list as the case may be)