Stand or sit. Find the extremes of very slumpy and then the opposite of extended or "military posture" and then rest in the middle. This middle position should allow your trunk to be over your hips, your shoulders resting at your side. Your shoulders will have a slight angle forward when they are in neutral. This is correct, but it's quite easy to get to forward. Be attentive of this. If you are over corrected or extended, take a deep breath and on your exhale make sure you let your sternum relax or fall. This often can put you in that neutral position. If you are slumpy, try to think about lifting your ribs on top of your pelvis, like you are stacking blocks.