Speaking of air flow, your breathing is just as important to your singing. You cannot hold your breath to sing, so you need to learn how to breathe while you are singing. If you have to hold notes and you have not learned proper breathing techniques, you will notice that you are gasping for air long before the notes end.
You will need to learn how to take deeper breaths. Be warned that when you are first practicing this, you may notice a little bit of dizziness. Your body will eventually overcome this as you learn how to breathe more efficiently while singing.