Deep breathing exercises have been used for thousands of years to aid in relaxation and meditation. We bowhunters can benefit from the same feeling of relaxation if we learn to control our breathing during the shot.
Most archers instinctively take a big, deep breath and hold it in while they're aiming. I think this may actually cause them to wiggle a little more than usual because it increases tension in the chest cavity.
Other archers continue to breathe while they're aiming. This creates a lot of extra motion in the bow arm, and I wouldn't recommend it.
When I'm shooting in competition, I like to take several deep breaths before I draw my bow. This helps me relax, and it increases the oxygen saturation of my blood. If I have time, I like to do the same thing when shooting at game.
After several deep breaths, I like to take a final one as I pull my bow back, and then I let a little out to reduce the tension in my rib cage. I hold that final breath in until I release the arrow.