I just started doing them every day, one set as many as I could, whenever I was near the weight room. I worked my way up from 3 to 25, then decided to start playing with factors.
There are all sorts of rep patterns one can follow, so I just try different ones on different days, alternate chin-up days and pull-up days, or do a max set or a set of ten between sets of other exercises.
About a year ago I started adding weight. I could do a bunch with 10 lbs, and decided to see how heavy I could go after a few weeks. I worked my way up to two reps, clean form, with 90 lbs attached to me. My goal was 100 lbs by the end of the school year, but giving blood took the energy out of me for a bit, and I didn’t make it.
I’ve rediscovered rock climbing, and all the time I spent doing them is justified, as it gives me a huge advantage and ability that most other people I climb with don’t have.