When we look at the question how to breathe when running, we need to consider the role of the air that we breathe in and what its main purpose is. One of the main purposes of breathing is to supply the working muscles with freshly oxygenated blood to allow the muscles to contract continuously. The extent to which this happens will vary depending on the intensity of the exercise that is being participated in. Situations such as running in low temperatures and running very fast will have a bearing on the way you need to breathe.
One thing you must concentrate on doing is to breathe as deeply as possible because this fills the lungs as fully as possible. Think about breathing down to the depths of your belly so that you can feel your tummy rise and fall with each breath, not only your chest.