This isn’t super-scientific, but what I do is keep folders on my hard drive for each format that I teach. I have a bootcamp folder, a small group circuit folder, a MELT and yoga folder, and folders for Zumba playlists. I title each class with the format, location, and one or two keywords that relates to that day’s theme or equipment and the day taught.
HIIT YMCA kettle bells bands 3-3-19
MELT Ballys neurostrength 3-5-18
3-2-1 SAC Tabata circuit 12-12-18
I go back every once in a while and re-read, but not too often, so this system is easy enough and takes very little time. When I do my key words in my title well, I can find old inspiration pretty well.