Algorithmically generated playlists from my personal library with the occasional new song thrown in. Maybe, new songs introduced that my social circle is listening to.
That said, I'm recently back to listening to albums exclusively again, which mostly solves this for me. If a friend suggests a song or I hear something on the radio, I pickup the album and listen through. It's a great way to discover new stuff while avoiding the trash. My only real issue is that so many artists I enjoy are in the EP only stage of their career, so for those, custom playlists is the only way.