Daoist breathing is the basis for both qi gong and tai chi, as I enjoy practicing them. Both arts use the muscles of respiration to initiate and power their movements. As such, breathing is the foundation of practice, far more so than the prescribed order of the movements, or form. It is really quite simple, but as with any proper daoist idea, the more we practice it, the more we learn, the more we see our previous conceptions were amateurish grasping at best, and pedantic drivel at their worst. As with any exercise you learn about on the internet, consult your health care provider before attempting it.
Daoist Breathing:
Inhale: bring the abdominal/core muscles inwards while the chest expands.
Exhale: gently push the abdominal/core muscles outwards while the chest contracts.
The basic idea is to turn your body into a bellows. When the area above the diaphragm expands, the lower contracts, and vice versa. This stimulates the Vagus nerve, which engages the parasympathetic nervous system, the rest and digest (healing and wellness) aspect of nervous function. Just doing daoist breathing provides many of the health benefits of meditation, tai chi, and yoga. You can combine it with these activities for even greater results.
It is of paramount importance to not force your muscles or hold your breath, as doing so could result in injury. It is best to only exert about 70%.
Let the inhalation and exhalation flow together as do the peaks and valleys of a sine wave. Inhalation is a yin concept, so draw your abdominal muscles inwards to your center point, the spot 1.5 finger breadths below the navel, our center of gravity. This should be a gathering feeling. Exhalation is a yang concept, and the abdominal muscles should expand outwards from the center point; a spreading feeling.
Thus, if yin is inhalation and yang is exhalation, the diaphragm is that curved line delineating yin and yang in the yin yang symbol. The daoist classic the Dao De Jing explains qi as what happens between yin and yang, or the interaction between yin and yang. The myriad creatures all descend from the qi between the yin and yang of the One. In this regard, “qi work” could be understood as diaphragmatic work. In my experience, qi is best understood experientially, not intellectually. Therefore, if you want to know what qi is all about, my advice would be to ignore what people say (especially me!), and focus instead on what you feel while engaged with the breath. Trying to grasp qi with our mind will lead us to an illusion, a construct of cognition, which prevents genuine communion with this most interesting of concepts. Feeling our body with our heart, leaving our labeling devices out of the picture, is the way to go.