To ease confusion, become something of a note-taker. Find out your habits through a system of markings on the scorecard. The course map is your best friend for marking all kinds of shots.
I recommend drawing where your shots ended up on the course map, and marking spots in between with an abbreviation system.
If you want to get really into it, plan it out the night before! You could also add up the errant shots vs. shots within a certain range of expected outcome. Say you planned to hit a drive right-center and it went more center but a bit right, you might (or might not) count it as "according to plan" - every golfer has to decide an acceptable amount of error. For mid-range handicappers, making a plan can really help the, as players realize when they work back from the hole they rarely need driver. Sticking to the plan to use 3-woods is a maturing player's course management choice, and strokes can be shaved there, to be sure.
Put dots for putts below score. Slashes in an "x" for fairway hit (slash right) green hit (slash left). I also recommend noting if ALL putts are long or short. IF you only hit 2 putts long all day, you may want to adjust your putting approach to become more aggressive (unless you made all the rest!)...
You could create a system for effective visualization (you might realize you don't visualize putts, or drives, and that could be helpful information).
Another cagetory to analyze is super bad shots. We try to minimize these of course, but if we have a baseline number of really bad shots, we have something to work with.
How many good results come from bad swings? IF we're going to be honest about improving we have to be a little tough on ourselves when it comes to bad swings that had good results. Mark on the course map shots which were swung badly but had a good result (GR). I once hit a thin shot to 5 feet, but felt I had to mark GR. This isn't a bad thing - I realized I was doing this often on approaches from 160-180, and that helped my restructure my practice time to get down better at that distance.
If you can tell, mark how many thin or fat shots you hit. (T or F)
You can analyze your last 10 rounds front and back - do you tend to rock the front 9 and peter out on the back? Or do you take a few holes to warm up and charge after the turn? You might be surprised at what you find.
Generalities: Most golfers are short and right on approach, short in putting. Those are two things about 80-85% could focus on as meaningful metrics to measure improvement. Taking more club from the fairway and putting the ball to the hole or just past can yeild good results fast for the mid-range handicapper.
Try practicing a little more before rounds. Most golfers show up, hit a few putts and they are off! That is a great way to maintain, but difficult to improve! Good luck!