One way to increase your pull ups and chin ups is doing them for repetitions. One week your target reps can be anything have a set point. Continue to work every week. Get stronger! For example i started a few months ago increasing my pull ups. I went from 6 sets of 7 repetitions (42) to 7 sets of 15 (105) repetitions. Set a mark and work consistently.
I suggest doing this type of body weight exercises, 2 even 3 times a week. Once you develop endurance then you may apply some weight to increase strength.
I like to add chin ups and pull ups to just about every exercise. Good way to build endurance. Before you know it you will be doing 200 repetitions of chin ups and or pull ups. Eat well, train hard my friends.