Train three times a week. Mix it up. A few ways to do this:
-Once every two weeks, test max reps: Just chalk up your hands, climb on the bar, and give it all you’ve got.
-Practice a different method: Try density training (doing as many reps as possible in twenty minutes, using any set scheme you desire, of chins and some comparably difficult pressing exercise). Or try ladders: Do 1 rep, rest a bit, do 2 reps, etcetera, until you can’t do any more reps, than rest and start at 1 again.
-Or just practice: Do chins off whatever surface you can (tree branches, doors, etcetera), as many as you can, as many days a week as you can, without burning out. Don’t try to do any other chin training if you do this.
There are a lot of different ways to train chins; just about any method will get you up into the 10-15 max rep range. After that, you have to be a bit more careful with your training; search ‘ZEB’s champion chinning routine’ for more on this.