Calm and steady breathing does a great deal to improve your stage presence. It is hard to command the stage while your breathing is fast and shallow and your heart is pounding. I know how defeating it feels to have practiced and practiced but to audition or perform as if you had never looked at the piece, all because of stage fright and anxiety. You can find breathing exercises for anxiety all over the internet for this type of stage fright.
The best ones work with slow diaphragmatic breathing to gain breath control. I know all you wind players and vocalists out there know this, but for our string and percussion instrument friends, if you are not taking a deep enough breath, you really have no control over how fast or how much air comes out on the exhale. To master deep diaphragmatic breathing, which activates your parasympathetic nervous system,(the opposite of your fight or flight response), there are 3 positions to practice.
Laying down on your back – Sitting down – Standing up
If you put your right hand on your chest and your left hand just below your belt buckle/belly button, take a few normal breathes and feel if your chest is expanding when you inhale or if your stomach is expanding when you inhale. You want your stomach to be completely relaxed so that when you inhale your stomach expands because your diaphragm has expanded down below your rib cage to make room for the air to fill the lungs. Now you have control of the breath and how much air leaves on the exhale and how quickly it leaves the lungs. If your right hand is moving as you inhale then you are just taking a shallow upper chest breath which will not allow you to sustain and exhale long enough to slow your breathing to trigger your parasympathetic nervous system. Breathing exercises for anxiety really do work, but you have to PRACTICE them.
Here’s one that I like from Dr. Andrew Weil on breathing for anxiety.