Assume an inverted position hanging from the rings, with arms straight. Squeeze your legs together, you should be in scapula protraction & posterior pelvic tilt, the whole body engagement.
Maintain this posture and begin to lower yourself in towards the backlever position, controlling your descent as much as possible. When you reach the bottom position, tuck your knees in and pull your legs back through. Return to the inverted position and repeat for repetitions.