Happily, and to my surprise, I earned an "Expert" badge in Marksmanship during ROTC training in high school, and here's how.
BRASS: Breathe, Relax, Aim, Slack, Squeeze.
Take a breath and then let your muscles fall comfortably, do not rebreath until after the shot is taken,
Aim calmly and without breathing,
Pull the trigger ever so gently to take up the "Slack" in it, but do not fire,
Now fire, with a gentle further squeeze, fire.
It takes practice, but the steps are perfect, and do work.
The Breathe and Relax steadies your body and stabilizes you when you let your muscles fall comfortably.
Aim is self explanatory, and can happen better if you are very still and do not breathe,
Slack starts the firing process, but its a separate and necessary step to control the shot better.
Squeeze when the above conditions are all in symphony and don't hesitate.
I still amaze guys with my bulls-eye shots. lol