Cut a hole 4 inches in diameter into your target center mass, set target at 15 yards, and slap yourself upside the head each time you shoot and see a smaller hole anywhere on your target smaller than four inches.
For real, cutting a hole in your target and shooting thru the hole will get you off the idea of placing each round on top on one another.
As you get better, make the hole an inch smaller, move the target stand near and far, known and unknown distances, sideways on to where you're standing,etc.
Combat handgunning is getting multiple rounds around/in center mass at odd angles and unknown distances.
The hole method also saves your targets.
Works well for target shooting as well, hole is just smaller