The blade

When playing off your back in BJJ, I find it helpful to think of keeping one shoulder blade off the mat at all times. Being on bottom in theory should be an active game, where you use movement to set up attacks and lessen the chances of being attacked yourself. Being flat on your back increases the surface area and friction you will need to combat in order to move effectively. By keeping one shoulder blade up as a rule of thumb, you instinctively allow yourself more movement and more chances to attack and defend successfully.