Essential to all wind musicians is an understanding of diaphragmatic breathing. You need as much space as possible to fill those lungs! Working to develop your control over the air stream takes time and patience.  Watch this example of breathing to get a visual idea of what it’s all about.  Then, try a simple exercise–lay on the floor with a stack of heavy (but not too heavy) books on your stomach.  Breathe deeply to make the stack of books rise, then as you exhale keep the books elevated by pushing out your stomach.