There are different methods of breathing to practice depending on where you are in your cultivation. All methods make use of the mind-intent (will and focus) leading the breath.
The first method: Start by counting the breath. This consists of counting each exhalation only. Count up to ten exhalations and then start over, doing so repeatedly during the meditation time. If you become confused or distracted, return to one again until you can count ten exhalations without distraction during the entire sit. When using this method, constantly sense the breath and counting in the lower abdomen, using the mind-intent to bring the breath into the Dan Tian.
Once you have been practicing the first method for a while, you may experience one-pointed concentration, where time seems to disappear, with an hour feeling like just a few minutes or less. When you experience this, you are in the second stage of cultivating the breath, and you can move on to the second method.
The second method: Focus on sensing the inhalation and exhalation in the lower abdomen. Just be aware of each part of the breath, and always return to the method if you become confused or distracted.
After having practiced this for a while, you may experience True Breath wherein the breath seems to work of its own accord, with no physical effort required, and the breath seems incredibly full and active. It will also feel as though only a few breaths were taken during the meditation time. There may also be the sense of not wanting to get up when the sit is done. Once you have had this experience you have entered into the third stage and can move onto the third method.
The third method: Sense a small, white cloud or vapor-like substance just below the nose. Imagine that during the inhalation it is dragged in through the nose slightly, and expelled slightly on the exhalation.
Experiences & Challenges in the Final Stages
As you practice this third method, visualizing and feeling the vapor, you will begin to sense the source of the breath coming from the Dan Tian, not the nose. At this point, you have entered the fourth stage, wherein you may experience a sense of lightness of body and as if time itself is frozen, which initially frightens the practicer.
From here, you may begin to enter tranquility, the fifth stage, wherein there is only consciousness of the breath, not the physical aspect of breathing. An initial obstacle to entering this stage is the experience of the breath stopping altogether, and one usually panics and grasps onto the breath again. Concentration is then broken. This is very difficult to get past, as it is an inherent attachment to the concept of self and life. When there is no thought of the sit being over or even of when it started, this is Sitting and Forgetting.