“Sit solidly in samadhi and think not-thinking. How do you think not-thinking? Non-thinking. This is the art of zazen. Zazen is not learning to do concentration. It is the dharma gate of great ease and joy. It is undefiled practice-enlightenment.” (Dogen, Rules of Zazen: Zazen-gi)
Zazen, seated meditation, is the basic practice of Zen. In Soto Zen it is called shikantaza, just sitting. You will benefit from learning from teachers and masters, but finally, you have to experiment and test for yourself what is good for you, and what will help you towards realization. There are three dimensions to zazen: bodily posture, breathing, and mental attitude and vision.
Take a good, comfortable posture. Take a posture according to your physical conditions: full, half or quarter lotus, burmesian or seiza posture. You can also sit on a chair, preferably with some back rest for the lower back, your feet firmly planted on the floor. Let your whole body rest on the cushion and the floor. Keep your back straight, with lower back a bit curved forwards.
Let your head be held up, with chin a bit in. Let your shoulders be relaxed and the chest open. Hold your body loose and relaxed but steady, straight up and firm.
If your legs go to sleep, adjust a bit their position to relieve the pressure and avoid sleeping legs. Often you may feel a tension in some part of the body, particularly the neck, shoulders, lower back. Ease the part if it is cramped or held tight. But do not try deliberately to do something to that part of the body. Rather, after setting yourself at ease and being properly seated, just stay aware of the tension or pain.
Sometimes it helps to imagine healing breath being breathed in and out through that part of the body, and do not overdo it. If you think that your posture is not certain, ask the leader to check and adjust your posture. After that, just be, let be and be aware. Often when no thoughts bother you and you are in lucid concentration, your body will feel like being pulled in and contracted, or feel the heat; just let it be. Do not let yourself fall into a trance.
Hands and palms in the usual Zen mudra, resting close to the lower belly. If this is a strain for you, just hold your hands resting on your lap.
Let your eyes be slightly open and relaxed, looking down in front of you a few feet away, blinking as usual, without staring at any point. At times it is all right to close your eyes. Hence, keeping one’s eyes open calls one to be aware, to be here and now, to let be and be present to whatever happens to one.
During the kinhin walk, hold your body loose and flexible, be aware of your body and the walking movements, and be also aware of your breathing rhythm, eyes gently looking downward in front, hands in the kinhin mudra.
The way you breathe involves your basic attitude to life. In Zen one does not try to control one’s breath. One breathes normally but in a healthy way. However, focusing on the outgoing breath or exhalation is very helpful. Further, abdominal breathing is recommended. Focus on the out-breath, and breathe out long, slow and steady, and let the incoming breath flow normally and gently and of shorter duration. You can exhale to the count of one to ten; it helps for concentration or samadhi. After a while, such breathing will become normal and natural to you. Do not try to force deep breathing.
As the quote from Dogen at the beginning shows, zazen is not one of doing or achieving; it is not a method or technique. Zazen is not simply concentration or samadhi practice or getting into some trance state. The physical posture of zazen can be said to be the door opening into the spirit of zazen. But Zazen is more than a physical posture or a particular experience or a particular state of mind. Zazen is a form of healing affirmation, it is letting-be and be-ing. When you do zazen, it is the universe that is doing zazen, it is Buddha who is practicing. Zazen embraces all times and spaces and at the same time, it is timeless and spaceless.