There are also days where I just "listen", not caring much for technique, but rather playfully explore a piece or an idea.
The most important thing in my opinion is to not fall into the trap of just playing something over and over again, hoping for incremental progress, but instead find out what you can't do and work on improving precisely that. Playing the bars of a piece in reverse is a good way to get around this.
During the long practise I take that principle even deeper and use the time to work on the hardest parts (= the ones which aren't fun to play, because I'm not yet able to play them properly).