Also, while practice in very important, remember that practice doesn’t make perfect. It’s “PERFECT practice makes perfect.” More frequent practice shooting fewer rounds, but concentrating hard on what you’re doing, will be more productive than less frequent, higher round count practice.
Very important advice there.
If you start flinching, stop and take a break. Shoot a rimfire, dry fire, do a few push ups or take a nap. Don't practice a flinch.