Over at my Spotify account, I've gone the super-nerdy ex-record-store-worker route and organized playlists by year; this is a lot of fun to visualize what was happening when, both pop culture-wise and personally. Sure, sure, there are other, regular playlists I've made, but I've been coming back to my year-lists a lot, and am happy to discover new (or old) stuff whenever I can.
As for the playlists themselves, I adhere to a strict rule, based in my being raised on 60-minute cassette mix tapes: playlists can only be 10 songs or 1 hour long, whichever comes first. (Yeah, yeah, maybe it's not a strict strict rule, but whatever).
Also? I'm a sucker for the algorithms.