I put up a blog illustrating one of my favorite BJJ drills. You can see it here:
I would also recommend low angle pushup, where you really work that range with your chest a few inches off of the floor. Not only will it strengthen your shoulders, but it will also prepare you to maintain a low elevation and have your partner carry your weight. I go over some subtle mechanics of this in the last PMenu. The pressure game is really about isometric strength, so anytime you can suspend yourself, whether that's holding a position on a pull up bar or hovering a few inches off the ground, you're prepping your body for grappling applications.
Hope this helps!