I love chins and pull ups, and id say i could thank them for 50% of my back/bicep development.
I started a few years ago after reading something , somewhere that arnie wrote,
I did 50 chins/pullups 3 times a week, at first it was like 6 sets of 5 and 5x4,
Every week id progress cutting sets and adding reps. simaular to what kyle's suggesting.
Eventually i added weight on a belt ,
In my opinion its a better way than using a lat pulldown machine , witch unless you have very flexible shoulders its hard to do correctly, ( the amount of people i hear say they cant feel there lats working during a pulldown is ridiculas) .
Another good way to improve chins is to put your barbell in a squat rack alittle less than waist high, grab the bar with your feet stretched out infront of you, keeping your core locked pull your chest towards the bar.
Its a high rep exercise but , incline pull ups have merit for beginners trying to imrove chin up / pull up strength.
This is exactly what I do.