One needs to practice proper shot preparation and follow through.
From The NRA Basic Rifle Course Instructor's Guide:







It takes some concentration to aquire and maintain the sight picture throughout the entire shooting process. One recognized way to help obtain the sight picture and to hold it steady is that once you're in postion to shoot, briefly hold your breath just like you were going under water. At that time, you will try to acquire your sight picture without putting pressure on the trigger until the sight picture steadies. Then the trigger is pulled as gently as possible. If you can't aquire the sight picture during the 5, 10 or 15 seconds that you're holding your breath, either stay in postion and breath a little to feed your muscles some oxygen, or totally relax the gun while breathing and then get back into shooting position and start over.
Holding one's breath will help to steady the sight picture to take the shot and then follow through afterward by remaining steady for an extra second or two.
The recommended practice is dry firing the entire shooting sequence over and over.
Holding one's breath is not mandatory but it works better that way even if it's only for 5 seconds, and after a while it becomes automatic. The breathing at least needs to be slowed down since too much breathing will cause the sight picture to move back and forth.
A person also needs to keep their finger off the trigger until they're in postion, on target and properly prepared to fire.
Practicing follow through is really important.
When shooters use proper follow through, they can often tell where the shot has hit before they even see the actual hole in the target.