For me, it was concentrating on the sticky point that got me there. In my case, it was the initial pull that was the limiting factor. After I got that initial pull I could grind my way up all the way. That meant negatives and hanging out in that initial pull position during the negative.
So yeah, figure out what your sticking point is and attack that part head on.
ETA: I also ditched the band in favor of negatives. If a workout included 10 pull-ups, I would do 3-5 negatives.