People tell me all the time that they "did some breathing." While it's true that the breath is a simple key to stress management, the way we use the breath to accomplish this is rather diverse and more complex than meets initial presupposition. I like to think of the breath as tool and toolbox.
Who are you?
I have given several workshops on the breath in yoga, and I believe there is great benefit to first uncovering who you are as a breather. Do you hold your breath? Do you gasp, grasp for air, keep your shoulders up at your ears? Is your breathing shallow? Are you a mouth breather? Are you ever breathless? Do you inflate the chest before the abdomen when you inhale? You kind of have to undo before you start to redo.
A few breathing basics:
We use the nose to breathe, although releasing with an AHHH through the mouth can be relaxing
Not breathing isn't the same as consciously suspending the breath, which is known as kumbhaka. If you're someone who forgets to breathe, focus on exhaling before you go for a tempo with more holding in it. The above ahh breath is a great yoga therapy remedy, and here's a great way to practice: