The normal standing posture is one with the bare feet fully in contact with the surface. The legs are in an un-flexed position, the pelvis is level from right to left, the arms are held relaxed at the sides and shoulders are level and parallel to the pelvis. The eyes are in a horizontal level position as well.
From the lateral or side view, your standing posture should be one where the knees are unbent. The pelvis will have a slight forward inclination. Your low back has a forward curve or lumbar lordosis, the mid-back has a posterior curve or thoracic kyphosis and the neck has a forward curve known as a cervical lordosis. The head is carried over the shoulders. Viewing your body from the side, if you were to drop a plum line it would pass through the ear, side shoulder, middle of the pelvis and knee, and fall just anterior or in front of the ankle.
Standing posture is a "learned" unconscious dynamic action. Although you
are unaware of it, your muscles are in a constant state of flux
allowing for effortless balance and minimal muscular loading.
In some neurological diseases this mechanism is impaired and this person will demonstrate problems in this balancing act. This will manifest itself by causing the person to fall to one side or the other when the eyes are held shut.
You were meant to be in motion. Standing usually has no negative impact in the short term. However, prolonged standing or repeated episodes of prolonged standing can be detrimental to your health.
Standing can have adverse effects on the cardiovascular system, muscular system, joints and overall body health.
If there is a leg length inequality typically you will unconsciously position the long leg forward with a slight bend in it's knee and perhaps a lateral inclination or outward position. This is an unconscious effort to reduce the pelvic tilt and corresponding spinal curvature, thereby creating a more normal muscular balance and relieving muscular activity or overload and minimizing discomfort.