Lay on the floor on your back with a kettlebell. Roll to your side as shown. Let the kettlebell push your numeral head into the socket. This will also push your scapula towards the floor. To balance the kettlebell lock your scapula down to your ribs. Basically set your shoulder blade like your about to bench or pull your scapula into retraction.
Hold this for 45-60 seconds. Do 2-4 sets. These are great for a shoulder swarm up prior to an upper body day or later in the season as a finisher/ prehab.
Super heavy weight is not necessary. The athlete shown used a 20lb kettlebell our throwers (400 lb + benchers) would typically use a 50 lb kettlebell.