Stand in front of a mirror on a non-carpeted floor, feet together in a comfortable parallel, knees straight but unlocked.
A) With your weight evenly distributed, visually observe your posture and alignment from the front and BOTH side. Check from the front for tilted hips and shoulders (i.e. not parallel to the ground) See image below to help you find a comfortable (neither tense, nor slouching) alignment.
B) Transfer your weight to one leg (supporting leg), but ensure that there is no tension in the free leg (i.e. the foot will still have contact with the floor, but without any weight in it).
C) As before, visually observe your alignment, the position of your hips, ribs and shoulders. Note any changes you see in your pelvis and hips when you go from one leg to two and back to one.
Check from the front for tilted hips and shoulders as well as for any additional tension you may see or feel in your legs/supporting knee/neck/torso/arms and even hands.
D) Feel where the weight is in your foot;
i) move the weight around in your foot from side to side and ball to heal to FEEL what changes happen in your body and where you feel you can stand up on one leg with least tension.
ii) once you find that place tilt your head slightly forward and feel how your body compensates for the change. Return the head to neutral.
iii) now tilt your head slightly backwards and feel how your body compensates for the change.
QUESTION: Do you normally allow your neck free so that your head rests in neutral position or is it tilting back or falling forward?
E) Repeat D as above but this time refer back to the mirror to SEE what changes.
F) Repeat B to E on the other leg to SEE and FEEL differences from one side to the other.
This is a good start to help you perceive and understand your own body, postural alignment, imbalances and asymmetries. Though very tempting, don't worry about things being 'wrong' or you needing to 'fix' things by doing X and Y. The answer is usually to do with releasing tensions and allowing expansion upwards and outwards.
Your body is intelligent and knows how to remain balanced, too much unconscious mental interference and holding tight to places can only complicate alignment and health.
Healthy well balanced postural alignment is a delicate process. It is not something that can be 'fixed' immediately. Healthy alignment and body use is developed first by the continuous practice of self observation, followed by very gentle gradual modifications and more observation.
It's very important to understand that our perceptions can be false! Using a mirror or photographing/filming yourself can be very useful in this process as it helps to align your perception with the external reality.
Image from www.fitness-programs-for-life.com