The most important Fundamental of all is to be sure your gun works. A recently purchased used revolver seemed okay in most aspects except the cylinder lockup had a hitch. Upon actually shooting it, it worked fine for the first 10 rounds. After that, the trigger could not be pulled with the cylinder closed. As I suspected, something was wrong with the center pin spring and the center pin would not push the bolt into position when the cylinder closed. Moving the bolt into position before it will fire is fundamental to double action revolver design.
Upon examining it later, there was no center pin spring, hence the issue. Someone had obviously messed with it because the extractor rod came free quite easily. Fortunately, the sear/bolt spring for a S&W fit adequately and fixed the problem.
As my colleague, the late Paul Gomez, was fond of saying, “Shoot Yor ….. Guns.”
After repairing it, I used it for another form of progression in practice, increasing distance incrementally. Starting out at a close distance, marking your target after each string, and then increasing the distance gives you an indication of where your strengths and weakness lie. Knowing them gives you an idea of what to practice next.