Release all the tension from your body before you start stretching. This can be done by tightening and then releasing the major muscles, such as those found in the arms and legs.
Be aware of your breathing at all times. Stretching exercises are improved when all the components are put into effect at the same time.
Breathe naturally. You should breathe deeply, but don't take exaggerated breaths or hike up the shoulders toward the head, as this does not improve your breathing capacity.
Expand the rib cage and upper abdomen when taking in a breath (inhaling). This increases the amount of power available to you for movement, as well as increases the capacity of your lungs.
Breathe in through the nose and out through the mouth. It sometimes helps to make an audible sound when exhaling as this encourages relaxation.
Exhale during the exertion period of a stretch, such as when you are contracting (tightening) a muscle.
Inhale when releasing a stretch and returning to your original position.
Do not hold your breath during stretching exercises, as you deprive your body of oxygen.
Develop a routine for breathing and stretching by reading "Pilates For Every Body" by Denise Austin at Amazon.
Monitor your posture at all times. This improves your conditioning and enables the oxygen to make its way unimpeded throughout the body and to the muscles that need it.