1. Don't be afraid of the gun

This is the first most important thing to start with. All else is in vain if the shooter still feels threatened, uneasy, unsure, or timid of the gun in any way when handling and shooting it.
A lot of shooters may think they are perfectly comfortable and unafraid of the gun in handling it and using it, but the truth is that being comfortable with the gun goes far beyond just being able to make it go bang and knowing what it's going to do. Shooting the gun as opposed to making it go bang is what controlling the gun is all about.

A shooter should have absolute confidence in handling and firing the gun in every way, from trigger pull to breathing to maintaining a clear sight picture, the shooter should know they are in control. Feeling anything less is an impedance to consistent and proper shooting, and even to safety.
One of the biggest keys here, along with all other firearms, is being familiar with the gun and it's operation in every way. If you're not familiar with taking the gun down to it's smallest and most basic parts, along with being familiar with what those parts do, and the gun's weight, handling, and operation, you need to start now.