Go into the quadruped position (hands and knees) and put one hand behind your low back.

Slowly lower yourself until your shoulder gets close to the hand on the ground.

Then rotate the opposite way until the shoulder is as high as you can get it comfortably.

Your eyes and head shoulder be following the moving elbow as it goes up and down.

Breathe in through the nose as you go down.

Breathe out through the mouth as you go up. 

These movements should be slow and controlled, syncing your breathing with the movement.