Breathe through your nose. It is harder to hyperventilate when your mouth is closed, because you can't move as much air through your nose.
Loosen your clothing. Tight belts and waistbands, girdles, bras, and skintight jeans can all restrict breathing and cause shallow, upper-chest breathing.
Learn belly-breathing (diaphragmatic breathing) techniques, and practice them when you are not hyperventilating so that you can use the techniques when you need them. People who hyperventilate usually take shallow breaths, filling only their upper chest when they inhale.
Try different relaxation techniques and see what works best for you. For more information, see the topic Stress Management.
Talk to friends, family members, or a counselor to help you relieve anxiety. Keep a journal to help you focus on your problems and find workable solutions.
Eat a healthy mix of foods. Watch out for caffeine: drink less coffee, tea, and soda, and do not eat as much chocolate. For more information, see the topic Healthy Eating.