By colour

A very popular choice for those of us of the not-alphabetical-by-author persuasion. And it is very pretty, generally speaking. But when I tried it myself I found a few bugs: (1) Too many books have several colours on the spine, obviously. (2) The effect is a bit ruined if you have too many books of one particular colour. (3) It's too symmetrical for my taste after all.

But I did try it! The plan was as follows: Because my Sandman shelf is so heavy, it has to have one of the sturdier middle shelves. So I was thinking a core of black books, surrounded by a circle in rainbow order, white and multicoloured books to be exiled to the periphery. I started tearing books out of the shelves:
I was even going to micromanage: black books that also had colours on them should stand as close to the corresponding colour as possible. Then I put them back roughly where they would go:
Then I started with the proper, detailed sorting. My thoughts about nuances quickly crashed and I went for the more asymmetric idea, and it was working really well for a while. Until I realized that (1) it is too asymmetrical after all and (2) I own far too many blue books. Far, far too many. It became a indigo-violet hole, sucking in all the energy of the room. (The picture doesn't do it justice.)
So I gave it up and started on another system: alphabetically by first sentence.