Having some video of you shooting is a good idea. I saw some things I was doing that I did not realize I was doing after I saw some video of myself.
The ole saying, a picture is worth a thousand words.
What I did was keep notice of what shots and from where on the table I would miss during tourney's. I would then practice those shots.
Sometimes where the shot is positioned on the table is what makes a normally simple shot a tough one.
There are what I call the 5 basic shot types. Those are straight, cut, bank, carom, and combo's. In each of the 4 groups, there is a endless variety of that type.
After the 4 basic shot types follows the hybrid shot. Those are any combination of the 4 basic shots types. Such as a banking a ball into a ball that's hanging in the pocket, a bank carom. Once again, the variety of hybrid shots is endless.
Then there is where the shot is located on the table coming into play. Didn't get that position just right and now the CB is frozen to another ball and so on. Once again endless variety.
The above is what I realized after awhile. I also realized the need to understand every aspect of a shot in order to accurately understand what I was doing right and what I was doing wrong and how the table was playing. Every aspect includes spin, balls used, table conditions, humidity, heat/cold, noise, lighting, and so on.
I do only two types of drills now. Single ball or 15 balls.
Single ball drill is used to learn new shots, to see what I'm doing wrong, just trying new things and not really caring about position, or really making the shot. Just doing things to see what happens. Free play time if you will.
15 ball drill is another matter. This is where everything matters especially position and where I hit the mark for the CB/OB. My standard for a good shot in this drill is 1) The CB goes where I want it to, 2) The OB hits center pocket, when I'm going for a pocket, or stops where I want when play a safe. It is important to have a standard to measure too. To me, close is not good enough.
The reason I find using all 15 balls just randomly placed on the table a benefit is that this provides the endless variety of shots needed to practice the basic shots and the hybrid shots. I could never have imagined some of the shots that have come up in using this drill.
If you use this drill, the key is looking for the basic and hybrid shots. Do one 15 ball session doing nothing but cuts. Another just banks, another doing caroms and then mixing that up.
This will also show you what type of problem you are having and this is where the single ball drill comes into use. Once you know the problem shots, just set up that shot and practice it, using different types of spin and speed until you get the hang for it. Then go back to the 15 ball drill to put it to use.
Anyway, this has been my approach to developing my game.