Breathe in through your nose, and pull the air in to your lungs using the diaphragm -- the muscle that enables your lungs to expand and contract. Imagine you are yawning, and take in a deep breath. The muscles that controlled the expansion and relaxation of your stomach are the diaphragm muscles.
Relax your body, and maintain proper posture when singing. Stand or sit up straight, with your legs spread equally apart. Keep your shoulders back and relaxed, and relieve any tension in your body -- especially the throat, jaw and face area.
Take in air for four beats, and then breathe out consistently for six beats. Breathe at a slow tempo of about 60 beats per minute, and maintain a steady airflow. Control your breath so that at the end of six seconds you are completely out of air, exhaling a steady and consistent stream of air. Practice exhaling in intervals of six, eight and nine seconds.
Sing a single tone, and hold it for four beats. Then, breathe in for four counts, and sing again for four beats. Continue this exercise to get used to taking in a full breath of air and connecting your voice with the breath -- so that you don't stop the stream of airflow before you sing. Instead, you breathe in and then -- without holding or stopping the breath -- you immediately breath out and start singing simultaneously.