The most common breathing technique is a 3:2 inhale-to-exhale ratio; Breathing should incorporate a full inhale and full exhale. This means you INHALE on the LEFT, RIGHT, LEFT foot strikes and EXHALE fully on the RIGHT, LEFT foot strikes. This pattern is not that hard to turn into a habit, however it is likely that it may require you to slow down your running pace for a few runs in order to fully habituate the technique. You will notice your heart rate decrease significantly for the same work load because you are now able to get more oxygen in and also to push more carbon dioxide out of your body. You may notice that you naturally drop to a 2:1 ratio when you run at a pace that is very difficult for you. That is OK. But realize it is difficult to maintain a pace that requires you to breathe at a 2:1 ratio.