If saints and self-enlightened sages lack great compassion, they are not the same as the buddhas and patriarchs, who considered great compassion foremost and sat in meditation with the vow to save all sentient beings. If the ancient meditators in India had attachment to their experience, false views, or conceit, their sitting meditation was not that of the buddhas and patriarchs.
What I mean to say is that buddhas and patriarchs, from their very first inspiration, sit in meditation with the vow to gather together all the qualities of buddhahood. Therefore in their sitting meditation they do not forget sentient beings, do not forsake sentient beings - they always have loving thought even for insects and vow to rescue them. Whatever virtues they have, they dedicate to all; therefore the buddhas and patriarchs are always in the world of desire practicing meditation and working on the way. In the world of desire only this world provides the best situation. Cultivating all virtues one attains to gentility and ease of mind.
If you want to sit in meditation, first find a quiet place and spread a thick mat for comfortable sitting. Do not let wind or smoke, rain or dew in. Keep a clear place to sit, with enough room for your knees. Although there were people who sat on diamond seats or boulders in ancient times, they all had sitting cushions.
When sitting in zazen your body may seem hot or cold, uneasy or comfortable, sometimes stiff, sometimes loose, sometimes heavy, sometimes light, sometimes startled awake. This is all because the breath is not in tune and needs to be tuned. The way of tuning the breath is as follows: open your mouth, letting the breath be long or short, gradually harmonize it. Follow the breath for a while; a sense of awareness will come and then the breath is in good tune. After that let the breath pass naturally through the nose.
You may sit with legs crossed or underneath you. Loosen your clothes and straighten them. Place your right hand on your left foot and your left hand on your right hand, with your thumbs together near the body about the level of tanden - about 2 inches below the navel. Sit up straight, without leaning to the left or the right, front or back. The ears and shoulders, nose and navel should be aligned. The tongue is kept on the roof of the mouth, and the breath should pass through the nose. The mouth should be closed, while the eyes should be open, though not too widely, or too slightly. Having attuned your body in this way, breathe deeply through the mouth a couple of times. Next, sitting steady, sway your body seven or eight times, going from larger to smaller movements. Then sit upright and intent.
Cast off mind, intellect, and consciousness. Cease recollection, thought, and observation. Don't aim at becoming a buddha, don't be concerned with right or wrong; value time as though saving your head from burning. The Buddha sat upright, Bodhidharma faced a wall, singleminded, without any other concerns at all. Shishuang was like a dead tree. Rujing admonished against sleeping while sitting. "You can only succeed by just sitting, without need to make use of burning incense, prostration, remembrance of buddha names, repentance ceremonies, reading scriptures or ritual recitations," said Rujing.
Always abide in great compassion, and dedicate the boundless power of sitting meditation to all living beings. Don't become proud, conceited, or self righteous - these are qualities of ordinary people.
Just sitting, not doing anything at all, is the essential technique for penetrating zen. With body and mind at ease, behavior harmonious, abandon worldly feelings and don't cling to feelings of the way.
Keizan Jokin (1264-1325)
Taken from Timeless Spring: A Soto Zen Anthology, Thomas Cleary (out of print)