I think breaking down everything is a good idea! What I'm doing is that I analyze a course by looking at what was great and what was wrong, then I visualize the course in my head and I do it again mentally by telling me " open your inside rein, inner leg, put your hand down...".
I often do this before a show, the day before, I watch the videos and I redo several courses in my head by closing my eyes 🙂
I think you have to be critical.
Look at your position, the action of your hands, your legs, the action of the horse, the quality of his movements and jumps if it's jumping.
You have to shell the slightest second and every movement to see if it is perfectible. You can do this exercise by being next to your trainer to help you understand or perceive flaws.