How To: Breathe properly while running

Breathing oxygen is an extremely important component of staying alive, right? Well, the same goes for running. If you're not breathing properly, you're running is going to suffer.
The most important thing is that you breathe comfortably. Do what feels right. Your body breathes instinctively - even while you're sleeping, your lungs and corresponding muscles are going through the motions. Running while breathing does not have to be complicated. As long as oxygen is entering your respiratory system, you're doing okay.
How you're running directly affects how you're breathing. When I'm running fast, say a 7-minute mile pace, I'm breathing mostly through my mouth. Your mouth provides a much larger port of entry than your nose, and it's the most effective way of getting oxygen into your system quickly. However, when I'm running super-long distances at a 10 to 12-minute pace, I'll let my nose handle some of the intake.
Breathing through your nose is a great way to give your lungs a workout and increase capacity. Try this next time you're on a long distance run: breathe in through your nose only and exhale through your mouth.Yes, it's more difficult than mouth-breathing. But if you stick with it over the course of a few weeks you'll notice that your lungs are retaining oxygen more effectively. Once you feel comfortable inhaling through your nose and exhaling through your mouth, try switching to all nose for a few minutes at a time. This requires more effort, but will strengthen your lungs even more. Before long, you'll notice your breathing taking on a meditative quality. It will be automatic and out-of-mind, leaving room to focus on other aspects of your running technique.
Lastly, you might want to try belly breathing. I've found that if I periodically take very deep, voluminous breaths during long distance runs - I'm talking about a big 'ol breath that expands your stomach to Buddha proportions - it engages my body's core and helps circulate energy from toes to fingert