Support yourself on parallel bars with straight arms. Lower your body until your elbows reach 90 degrees or slightly below, then push back up. Keep your chest slightly forward for chest emphasis, or upright for triceps focus. This is one of the best upper body builders in calisthenics. If you can't do them, regress to bench dips. Build up to 3 sets of 8-12 reps. Master this before attempting ring dips.