Rather than trying to touch the bar to your chest or reaching your chin over the bar (both of which can produce dysfunctional mechanics), the goal should be to achieve proper upper back and lat activation. This requires several components.
The best cue is to keep your shoulder blades back and down. The first few reps show the incorrect position. In the last few reps, the shoulder are back and down.
We don't throw around the term "living legend" much around here because not many people deserve such accolades. But T-Nation recently sat down with a man who just might fit the bill: Dave Draper.