The slave kneels and sits on heels with back straight, knees widely spread, breasts/chest forward, head up (usually to the left) and palms resting on thighs.
Common variations include turning the palms up (usually to demonstrate extreme vulnerability, a desire to be used, and/or placatory behaviour) and lowering the head.
This is the position slaves are expected to assume when entering the presence of, approached by, or commanded by the free. It is the most common slave position and one in which you will likely spend more time than any other.
The commands, "Kneel", "Nadu", "Position" and "To your knees" all refer to this position, as well as the hand signal with the first two fingers pointed down in an inverted V. Typically, the fingers will be pointing at the location in which you are to kneel.