THE LADDER METHOD
For your first set, perform half your max number of pullups. (For example, if you can do 10, perform only five. If you can't do more than one or two, see mensfitness.com.) Rest 30 seconds, then perform one more rep than you did in your last set (in this example, six). Continue resting and adding a rep in this fashion until you can no longer perform a full pullup with good form. At that point, go back down the "ladder" by performing one less rep than you did on your last set, resting the same time between sets. Continue until you're back at the number of reps you did on the very first set. Do this twice a week. In each succeeding week, try to do one more rep on the set you got the most reps with going up the ladder. When you reach your max number of reps in this fashion (in this example, 10), complete your next workout with a 10-pound weight attached to your waist.