Re: Breathing exercises
For me personally, I found zazen to be extremely helpful.
I find it very difficult to concentrate on my breathing during more complex activities (such as normal training) because so there's so many more pressing issues to think about. I have only so much mental ability to work with, and breathing is such a low priority (since it's an automated behavior) that it tends to get dropped. And even if I can spare some mental focus for breathing, proper breathing training is a rather subtle thing, IMO, and I don't feel I get the full benefit.
Since breathing is an automated behavior, IME, it requires a certain amount of mindful, dedicated practice to overcome and "re-wire" your ingrained habits. Zazen gives me that. I'm sure some sort of modified-zazen breathing practice would do the same.
If you don't want to practice full-fledged meditation, you can try this---sit in a chair with good posture and a straight back, arms resting on your thighs. I suggest you practice in silence, but some non-distracting music would probably be fine. Breath in and out through the nose (breathing in through the nose and out through the mouth is OK too). Try and breath with your lower belly rather than your chest; it might be helpful to wear some pants with an elastic waist, as the slight pressure will give you some bio-feedback on whether you're doing it right or not. Also try to breath fully, that is, try and fully fill and empty your lungs with every breath. If you breath fully the actual speed of your breath isn't so important (breathing fully will naturally slow down your breathing). Think about every breath, be very mindful of what you're doing. If your mind starts to wander, just go back to your breath. Keep doing this for like 20 minutes.
IME, if you do this daily (or 5-7 times a week), you should start to see your breathing patterns change during your day-to-day activities after maybe 2-4 months.