You should be synchronizing your breath with your steps. I think the specifics are different for everyone, but I inhale every two steps and then exhale every two steps. This helps you get into a rhythm, and you end up concentrating less on being out of breath. This is why I like running long distances because I feel like you're able to get into a much better rhythm. It takes time to get into that sort of breath and step rhythm, so don't get discouraged. Go on youtube and watch some videos about it, they can be extremely helpful.