Running being an intense exercise it requires more oxygen and proper breathing allows more oxygen to enter into lungs and muscles.You should do Cadence breathing, which is best for running, i.e. 3-4 steps inhale,then next 3-4 steps exhale.Avoid protraction of your shoulders while running,expand your chest and shoulders and keep your back straight to increase the air entry into lungs.Start slow by doing just a brisk walk or low intensity mild exercises like stretching and gradually increase your pace.