The truth is two-fold; Practice and Gun.
You will never get there without practice. You are over-thinking the process. This is required when you start but with practice, this becomes a smooth muscle movement. Practice, practice, practice!
The second is your choice of firearm. I simply can not shoot a glock accurately. I've owned a 40 cal M22 since 1985 and can't put three rapid fire holes in paper!
I hate the 40 S&W round. nuf said!
There are two types of shooting, competition and fighting.
I think your interest is in personal defense and therefore fight shooting. And in fight shooting we do not worry about shot groupings, just shot placement.
My mantra is one used by the old-timers, "..multiple traumas to multiple systems...."
more holes means more blood leaks out! Drop the blood pressure and you drop the target!
This is the results of my last range visit. It's a little drill called Mozambique.
This drill consists of shooting two rounds to the center of the torso, followed by a shot to the head. Under nearly any conditions, engaging an assailant with the Mozambique Drill should offer a high probability that one's assailant will be stopped and likely killed.
Try this read:
And practice, practice, practice!