Set-up: Grasp a pull up bar with one arm, prepare to rock and roll.
Lift: Bracing through your core, lift yourself up until your chin is over the bar, trying to get as high as possible. Cue yourself to pull your chest to the bar to ensure full height. Attempt to descend all the way to full extension as this will engage more of the shoulder stabilizers and muscle mass of the back.
Emphasis: Do not swing your body up to the bar.
Strength criteria: The one arm pull up is obviously an advanced strength exercise, and should not be attempted until suitable progression achieved. In particular, you should be able to perform assisted one arm pull ups for reps.