Find a relaxed breathing, take a deep breath. When the lungs are half full, pause and squeeze the trigger.
Take a few deep breaths, let some air out – pull the trigger.
Focus on finding a relaxed breathing and a heart rate as low as possible. Exhale slowly and pull the trigger. Regardless of which method you prefer, a good ground rule is to never end up in shortness of breath, something that makes it easy to force. Instead, take the gun down, breathe, and start over. Good luck!