Jundo says: Zazen is a perfect non-doing, even when imperfectly done.

However, good balance in body yields good balance in mind.

Yonotsune zasho niwa atsuku zamotsu o shiki, ueni futon o mochiu,

aruiwa kekkafuza, aruiwa hankafuza.

Do not aim to become a buddha. How could it be connected with sitting or lying down?
Usually on the place where we sit we spread a thick mat, on top of which we use a round cushion. Either sit in the full lotus posture or sit in the half lotus posture. To sit in the full lotus posture, first put the right foot on the left thigh, then put the left foot on the right thigh. To sit in the half lotus posture, just press the left foot onto the right thigh. Let clothing hang loosely and make it neat. Then place the right hand over the left foot, and place the left hand on the right palm. The thumbs meet and support each other. Just sit upright, not leaning to the left, inclining to the right, slouching forward, or arching backward. It is vital that the ears vis-a-vis the shoulders, and the nose vis-a-vis the navel, are directed away from each other. Let the tongue spread against the roof of the mouth. Let the lips and teeth come together. The eyes should be kept open. Let the breath pass imperceptibly through the nose. [NISHIJIMA]

Have no designs on becoming a Buddha. How could that be limited to sitting or lying down?
At your sitting place, spread out a thick mat and put a cushion on it. Sit either in the full-lotus or half-lotus position. In the full-lotus position, first place your right foot on your left thigh, then your left foot on your right thigh. In the half-lotus, simply place your left foot on your right thigh. Tie your robes loosely and arrange them neatly. Then place your right hand on your left leg and your left hand on your right palm, thumb-tips lightly touching. Straighten your body and sit upright, leaning neither left nor right, neither forward nor backward. Align your ears with your shoulders and your nose with your navel. Rest the tip of your tongue against the front of the roof of your mouth, with teeth together and lips shut. Always keep your eyes open, and breathe softly through your nose. [SZTP]