I think that keeping track of workouts and saving that information for years may be an overlooked tool in your training. Even for someone who isn’t super serious, like myself, it is fascinating to look back over training periods and to learn from it.
There are far more sophisticated methods, and ways to really learn in depth, but simply keeping track of your workouts and how you felt that day is something I have found useful and interesting.
Below is the document I use. I should probably use it all the time, but so far have only used it when following a training plan. I indicate both what I did for a workout, but will also include other notes about it; and overarching things for the day off to the right hand side.