Even before I quit, I had already been using breathing exercises and paying attention to how I breathe because of my lung issues. The more I work on my breathing now, the more I realize that smoking really screwed up my normal breathing pattern. When I would take a drag, my chest/belly would sink in, then when I would blow the smoke out, my chest/belly would go out. This is exactly the opposite of normal/calm/healthy breathing, when your diaphragm contracts and descends as you inhale and your belly gently pushes out. Then when you exhale, your diaphragm relaxes and lifts and your belly relaxes and sinks back in. Sorry to get all clinical, but this was a big deal to me to learn how to breathe correctly so my body can get the oxygen it needs. Breathing deliberately has also been a big help in conquering cravings and making me feel like an Ex instead of still breathing like a smoker.
I found this excellent book that has tons of breathing techniques for different situations/outcomes and explains how important breathing is to every aspect of a healthy body and mind. Maybe it can help someone else too.
