In translation zazen simply mean to sit (za) in zen. While zazen is not intended to be comfortable, its focus is not on physical endurance. So it is best to find a way to sit that suits your body. Usually a zafu (meditation pillow) or seiza bench are used to aid in sitting. There are several generally accepted ways to sit - of primary importance is sitting in stillness.
In the Burmese Position you sit cross-legged with the feet drawn in quite close to the body. Weight is equally distributed down through the spine and the knees. A zafu slightly elevates the posterior.
The Half Lotus Position begins similarly to the Burmese Position but the foot of one leg rests on the thigh of the opposite leg. The zafu again elevates the posterior to create a triangular base of the spine and knees into the ground.
The Full Lotus Position has the legs crossed with each foot resting on the opposite thigh. This requires some flexibility and will provide a naturally balanced triangular base.
Seiza (literally correct-sitting) is acceptable though it can be demanding for the extended periods of zazen meditation requires. A seiza bench can be used to relieve the weight of the body from the knees
Consistent across each form of sitting is the upright posture of the back. The chin is slightly tucked in, and the crown of the head is upright as drawn by a taught string. The mouth is kept closed with the tongue pressed gently against the front upper teeth. Breathe slowly and softly without effort. Exhale - the lungs will refill themselves. Keep your eyes half-closed - neither seeing nor not seeing.
During sitting the hands are placed in a mudra. For the Cosmic Mudra or hokkaijo-in place your right hand in your lap with the palm up. Gently set the left hand into it, also palm up. Touch the tips of the thumbs together lightly - they are neither raised nor lowered, forming neither a mountain nor a valley.
The Hannya Shingyo or Heart Sutra is chanted at the beginning of zazen. It is a Japanese adaptation of a classical Sanskrit text. The purpose of the recitation is to activate proper breathing and to state the intent of the meditation: in emptiness no form, no feelings, perceptions, impulses, consciousness.
After a recitation of the first line ma-ka han-nya hara-mita shin-gyo by the jiki (practice leader), all sitting participants join in the chant. The first several lines are recited at an increasing tempo until settling into a steady pace. The pronunciation is phonetic with English consonants and Italian vowels. Each sub-hyphenate is expressed as a beat. You should chant with a full, strong voice. Don't worry about getting every syllable right. Keep with the rhythm established by the jiki and produce a powerful sound.
At the beginning of zazen, seat yourself on your zafu and place your hands in gassho (palms together at chest). The jiki will clap once and ring the inkin bell three times. Everyone will chant the Hannya Shingyo. Place hands in mudra and sit in stillness for the duration - typically twenty-five to thirty minutes. At the end of that time, the jiki will sound the inkin once and clap twice. Return your hands to gassho and bow forward touching your forehead to the floor. Rise slowly and with care as there could be some numbness in your feet or legs.
Little is required to practice zazen. In the dojo you can wear a dogi and hakama. You are also welcome to wear the traditional samu-e jacket and trousers or any loose fitting clothing that is comfortable, modest, and unadorned. Bring a zafu, firm pillow, or yoga block for sitting. A copy of the Hannya Shingyo will be provided.