Somewhat haphazardly. I typically listen to multiple genres in one session as well. What I usually do is if I hear a song I like that's not already in a playlist (or if I like it enough that I want it in multiple playlists), I'll chuck it in at the end of one. Then when I have downtime I play around with the song order so that I like how each song transitions to the next. I enjoy doing that as a way to unwind. This method isn't great if you're the type that needs everything organized all the time though since my playlists are usually in some level of a work in progress state! The names are very boring - P01, P02, etc. I also have some playlists that are more themed, for instance a road trip playlist with more upbeat songs. I'll usually play around with that one based on who is road tripping with me and what type of music I think they'll enjoy.