Being able to flex and extend the spine in the middle-back is vital for proper overhead positions. Without it, your low back breaks at the midline causing you to lose your bracing.
Therefore, a proper brace in the overhead lifts requires a mobile spine.
Kneel down with your right knee on the ground and right arm extended out against the wall. Then rotate your left arm around to the other side of the wall. It is okay to move your neck.
While kneeling down, place either your hand or forearm on the ground. Then with the opposite arm, reach to point your elbow to the ceiling.
Be sure to have the butt to the heels. This locks the lumbar in place.
Foam Roller Extension
Place one ankle on your opposite knee in order to lock your low back in place. Then lay on the foam roller with it in the middle of your back. Try to arch your body around the foam roller as much as you can–use a weighted object if you can to anchor yourself.
With your butt to your heels again, kneel down while having your elbows up on a chair or box. Then arch your upper back up and down without moving your hips.