in the army they stress over and over and over again to control your breathing. That's where I really learned to control it. It's true, you will shoot 100% better if you control it. Plus, when deer hunting, your adrenaline is pumping so to get your heart rate under control AND your breathing under control can sometimes be a task in itself.
...and on that day when my strength is failing, the end draws near and my times has come, still my soul will sing Your praise unending, ten thousand years and then forevermore!