I started using such an app (pings you each evening to choose your mood and select some tags that describe your day).
https://play.google.com/store/apps/details?id=net.daylio (not affiliated in any way)
https://play.google.com/store/apps/details?id=net.daylio (not affiliated in any way)
The other thing I've also been doing that I've found much more fulfilling is writing down a daily highlight at the end of each day. I just add an event to a dedicated calendar that summaries the best moment of my day.
It's been really interesting to look back over, and it's a great memory prompt, because it gives me a way of looking back at the enjoyable times throughout the year. I've been going for just over a year, and I really don't see any reason to ever stop!