Posture: there are 4 common meditation postures. Laying down, sitting on the floor, sitting on a chair, standing up.
Back: strait. Leaning forward when sitting, may invite the exchange of meditation with sleep and may also invite back pain.
Mouth: lips closed, small gap (rice grain) between the upper and the lower teeth,
Tong: tong touching lightly the roof of the mouth while resting on the lower front teeth.
The tong is a “barometer of stress”, vacuum in the mouth, is a sign of tension.
Eyes: preferably with eyes close. When eyes are closed the focus turns inside and chances for distractions is reduced. It is much easier to use the imagination when eyes are closed.