The Buteyko Method
http://www.normalbreathing.com/It's focused on breathing through the nose, and trying to breathe less volume of air per second 24/7, awake and while sleeping, by improving lifestyle factors like exercise, diet, and mental perception. In order to improve at a quicker pace, the buteyko method highlights the role breathing has on things like exercise and mental perception. It also explains a tool you can use to monitor how food affects your breathing, and therefore how it affects your health.
The entire method revolves around the medical theory that oxygen is the primary fuel for the body. We can go a long time without food, and a relatively long time without water, but not long at all without oxygen in our tissues. The buteyko method adds to the oversimplified notion that oxygen does this by itself, by explaining that oxygen in your lungs and blood cells cannot be released from your blood stream without carbon dioxide present to allow it to do so. Therefore, the oxygenation cycle is completely dependent on carbon dioxide levels in the blood. By breathing large volumes of air, carbon dioxide in the blood decreases, this is why hyperventilating makes someone faint (brain shuts down), because not enough oxygen can get to the brain, because the carbon dioxide role in oxygenation is depleted. The buteyko method allows someone to consistently improve their carbon dioxide levels over weeks, months, and years by changing to a healthier lifestyle. There is a test you can do multiple times a day called the "control pause test" which relatively accurately monitors someones internal carbon dioxide level when graphed on a chart over periods of weeks, without any special equipment (it's free).
Furthermore, all the information about the buteyko method on that website is free. He sells books, which contain the same information on the website in a more organized form.
One major example of learning about this method is that the buteyko method says that mouth-breathing while exercising (in the sense that most out of shape people do it) is a sign that you are pushing yourself too hard. Exercise should be mostly aerobic, in order to affect more areas of the body, and should be done with nasal breathing only. It also explains that the best temperature to exercise is on the cold side, even if you get hot and sweat, for the same nasal breathing reason. The reason nasal breathing is better is mostly because it is harder to inhale the same volume of air through the nostrils as you can through the mouth. The less air exhanged per minute, the higher the carbon dioxide in your blood. Your brain will never let you suffocate by will power alone, because it monitors the carbon dioxide level, not the oxygen level, in your body.
This is also, to me, proof that carbon dioxide is not a waste gas, but is the single most helpful byproduct humans naturally create. It means life for plants and animals alike. It is more important than oxygen because it is more scarce, and desperately needed. The bad side effects of things like car exhaust come from other nasty chemicals that come out of it, not the pure carbon dioxide.
The main problem with the buteyko method, and even the diet the buteyko method advocates (a nutritional ketogenic diet) is that both are not normal behaviors for modern developed-country mankind. The gap that desperately needs to be filled is a method which reconditions human behavior, by understanding the principles of animal (human) psychology and behavior, and how to manipulate that behavior. Relying on will power, dedication, and perserverence alone means that for the vast majority, outstanding success only comes after lengthy trials of failures or when scared into radically changing ones life (for example, when diagnosed with cancer, many people will find the drive to suddenly start regularly exercising and eating better).
Buteyko, a Russian doctor, noticed in patients that he cured, even from cancer, that eventually once they returned to a normal health state, a high percentage of them would eventually take it for granted and revert back into their old lifestyle habits, and the diseases would slowly come back. They would approach Buteyko again, and get cured again (if the disease didn't kill them first), and the cycle would continue. Buteyko did not realize it, but this highlights how desperately a psychological aspect of reconditioning a lifestyle is needed, something along the lines of a military bootcamp - which actually does tend to change most of the troubled teenagers who go into it who would otherwise likely become criminals or deadbeats or addicts into disciplined, physically healthy (although usually mentally brainwashed into violent) people. Buteyko method is a very lengthy process which must become a lifestyle, 24/7, with no breaks, otherwise all your efforts are for nothing. This is why it is mostly used for asthmatics and other serious conditions that have high motivations to keep up the work.
Another example of behavior reconditioning is religion (as a way of manipulating behavior) but that one relies on a much longer timeframe, capturing people early, etc, and is highly ineffective compared to how radically a military bootcamp transforms an adult persons behavior and perception in a short time.