At the top level, I have:

Artists
Books
Compilations
Humour
Soundtracks

Artists has each artist as a separate playlist. In here, each album by that artist has a separate playlist. When possible, the albums are sorted in order of release date. Artists are sorted alphabetically. Tracks appear in albums, in track number order.

Books just has "Harry Potter" in it at the moment. This then has a playlist for each of the books. The individual discs _do_not_ appear as separate playlists at this level.

Compilations generally just has album playlists in it. Sometimes I have labels/series as playlists in their own right, e.g. "Cafe del Mar" appears as a single playlist, with all of the volumes under that.

Humour is fairly freeform at the moment.

Soundtracks has each movie as a separate playlist.

This mirrors (exactly) the layout on my Linux box, making keeping the two sync'ed easy.