A while back a couple of freinds turned me on to Buteyko, a technique developed for asthma. Without having trained in the method I think it is pretty amazing stuff. I never quite got comfortable with taping my mouth shut at night to sleep but I do run with my mouth closed and that has been a revelation.
I am at the point now where if my mouth opens looking for air I am working too hard and doing something outside of my natural rhythm. Give it a try if you are a runner or a walker. It might serve you well.