I read an article on improving pull-ups from an olympian that talked about how to improve reps.
He said you should never do pullups to failure, always do 70% of your max, three sets a day, spread out over the day.
If you go to muscle failure you'll shock the central nervous system and will not develop the muscular strength
as efficient as developing your strength. Every two weeks, re-eval your max, and go up from there.
So if 10's your max, you would do 3x7 reps a day, for two weeks then check your max.
Also remember proper form, kipping (swinging) your body is not a pullup, some crossfit requires kipping (100 reps) but if you want to improve,
dead hang, pull yourself up, head over the bar, and come down all the way. one rep.