Right now, I feel like I need to post links about breathing, since so many people in this site, including me, have breathing problems.
Three breathing exercises to reduce stress:
Breathing: Three Exercises - Dr. Weil
An exercise for relaxed breathing (Lately, I've been suffering from first-note anxiety, so I believe this exercise will help me with it):
A good linke about how a diaphragm really works (This really cleared me up about the diaphragm and its function):