The bear crawl has become of my absolute favorite exercises for shoulder health due to the fact that it not only hits the serratus anterior (which is often neglected in comparison to the traps), but it also hits it in closed chain while promoting scapular upward rotation. In particular, the reverse bear crawl is my favorite due to the active scapular upward rotation as you push yourself backwards.
I've shown a brief progression to working up into the reverse bear crawl. Make sure to really drive your hand into the ground and push THROUGH it to move your body backwards. Another cue worth trying is to think of driving your elbow forward.