" He had taught me to do just as he was doing, to draw the air in deeply and slowly to the bottom of my lungs through my nose, while expanding the diaphragm.  Then, after holding it momentarily, he slowly pushed the air out of the lungs by drawing the diaphragm in.  He explained that it’s important to let the air out through a relaxed and slightly opened mouth while keeping the tip of the tongue pressed lightly against the ridge behind the front teeth, with the tongue touching the roof of the mouth. "

― , The Art of Mental Training - A Guide to Performance Excellence