The pace of your breathing is closely linked to your mental state. The mind is at its clearest when breathing is calm and rhythmic. In contrast, it is very, very difficult to think clearly when your breathing is ragged and heavy.
An effective way of controlling your breathing is to use the rate of your opponent’s breathing to pace yours. When in a static grappling position (e.g. side mount), try to listen to your opponent’s breathing – if it is at a harder and faster pace than yours, chances are he is using a lot more energy than you, and subsequently he will tire more quickly.
At the same time, if you are breathing harder and faster than your opponent, you will probably tire sooner than him. In this case, it is best to slow your breathing down. This will naturally calm your mind and allow you to think clearly. It will also reduce the overall level of muscular tension in your body. These two effects in combination will allow you to remember your techniques and perform them fluidly.
Also, try to avoid inhaling before having completed a full exhalation. Ideally, empty your lungs completely, and pausing for a second before taking a deep breath to the bottom of your lungs, allowing your abdomen and rib cage to expand. By doing this, you re-balance the ratio of oxygen and carbon dioxide in the blood.
An efficient way of doing this is by adopting percussive breathing, which involves normal inhalations followed by several short, sharp exhalations. These exhalations are the result of rythmic diaphragmatic contractions. Many who have sparred with the great Rickson Gracie report having heard him make the ‘tss…tss….tss’ exhalations that are the hallmark of percussive breathing.
Unconscious holding of the breath is another habit which should be avoided. Man is the only mammal who does this. It causes unnecessary tension in the body and quickly results in chronic fatigue.
Before a match, you may want to try hyperventilating for a minute or two. This will hyper-oxygenate your blood and allow you to perform at your maximum capacity for a short while longer than usual. If you begin to feel light-headed at any time while attempting to hyperventilate stop immediately.
There are many supplemental methods which will help you learn how to control your breathing, my favourite is free diving.