Mix grip chin ups 

pull to the hand which fingers grip under the bar (supernate grip)
initiate the pull by bringing the shoulders down from the ears, with more focus pulling the chest and head up to the main working arm.
as you pull, make sure you shift your weight over so that the chin stays vertically inline with the fist,
drive the elbow down towards your stomach.
keep pulling until you bring the chin over the fist at the top.
follow the same pathway down, pause at the bottom of the active hang, before resting and starting again.