An Organized Body
You may have noticed that almost all of the movements you do require the same, general torso position. This is easiest to see in the slow lifts like back squat and deadlift, but trust us, you can use the same basic truck position whenever you have a weight in your hands.
Shoulders should be back and down, pinned to the lats. Another way to say this is that they should be externally rotated. To get an idea of what that feels like, stand up, hold your hands out to the side like the bottom of a snow angel with your palms facing forward. Take a deep breath, keeping your shoulder back from there, let them slide down your back. Your shoulders should be back without you pinching the shoulder blades together or holding your shoulders up by your ears.
Your abs and glutes need to be on- not clenched tight, just on. Find the top of your hip and bottom of your ribcage; place one thumb on each spot, extend your hands out from your body with palms facing down. Draw your ribcage down to your hip until both hands are parallel with one another and the floor. Compressing your ribcage will activate your abs and drawing your hips under you will activate your glutes.
Now, in this position, you can do anything! The differences in most movements comes from angles between joints and positions of your body in space, not from any change in good spinal positioning which is the basis of all good movement. If you are not in good spinal position, you are not using your body efficiently and you run the risk of injury. Good spinal position takes practice- try it while you type, walk, or watch TV. Then make sure that when you touch a weight your body automatically snaps into position.