My best was 15 at 200 lbs. I started out not being able to do any. So I did negatives using a box, and jumping to the up position. Eventually, I could do sets of 1-3. Once I got to 5 or so, I started adding weight. Once you can do chins with bunch of weight strapped on, higher reps are easy.
I'm not sure about the grease the groove method, never tried it. But adding weight works, plus you get cool muskelz.