The following exercise may make you feel tired at first, do keep at it as you will begin to notice that it takes less effort to breath, less energy is used when breathing plus it helps you learn to co-ordinate the diaphragm and abdominal muscles when breathing.
To find out if you are breathing correctly, place a hand on your belly button. This area should expand first when you breathe in and then spread upwards until your chest is expanded (don't lift the shoulders or push the stomach out). If you feel you are not breathing properly, practice the following exercise.
Lay flat on your back.
Place your hands on your waist, fingers pointing towards your belly button.
Focus on filling up your stomach from the bottom to the top taking a slow deep breath. (The aim is not to fill yourself to bursting but to inhale enough air so that you can feel the difference between a shallow breath taken when breathing from the chest).
You should feel your stomach rise and your hands being raised gently up and outward until you feel your chest expanding. The expansion is not only at the front of the body but also to the sides and back as well.
Breath out slowly to a count of 5
Repeat the exercise 10 times
Practice daily before you rise in the morning and prior to sleeping at night for 5 - 10 minutes gradually increasing this to 3 or 4 times a day.
Once you get it right, practice as often as possible, sitting, standing and whilst at work until you are breathing naturally from your abdomen.
Try the following exercise to help increase breath control - Count on one breath singing each number out loud. using one breath at any comfortable pitch. Start with a small number like 5 or 10 and increase this gradually until you can manage 25 or more without straining, tensing or running out of breath.