Allow one’s exhalation to flow out naturally and one’s inhalation to enter the body freely.

Exhale so as to reach the far ends of the Universe and inhale so as to concentrate our breath infinitesimally to a point in the lower abdomen.

Reference:
Ki in Daily Life
by Koichi Tohei
ISBN 4889960716

p.68

ZEN, Teaching of zen, Shodo Harada Roshi in America 1/7 youtube.com

The True way of Zen by Shodo Harada. Harada Roshi is a Rinzai priest, author, and head abbot of Sogenji Zen temple in Okayama, Japan.

Videos:
ZEN, Teaching of zen, Shodo Harada Roshi in America 2/7 youtube.com
ZEN, Teaching of zen, Shodo Harada Roshi in America 3/7 youtube.com
ZEN, Teaching of zen, Shodo Harada Roshi in America 4/7 youtube.com
ZEN, Teaching of zen, Shodo Harada Roshi in America 5/7 youtube.com
ZEN, Teaching of zen, Shodo Harada Roshi in America 6/7 youtube.com
ZEN, Teaching of zen, Shodo Harada Roshi in America 7/7 youtube.com

Links:
Shodo Harada wikipedia.org

Books:
Zen Mind, Beginner’s Mind
Shunryu Suzuki
ISBN 0834800799

Nothing Special: Living Zen
Charlotte Joko Beck, Steve Smith
ISBN 0062511173

Walking Meditation
Thich Nhat Hanh, Anh-Huong Nguyen
ISBN 1591794730