If you can do a pull-up, try modifying the traditional technique by draping two gym towels over the pull-up bar so both ends of each towel hang down. Then perform your chin-ups and pull-ups gripping the towels, not the bar. This poses a greater challenge to the strength of your hands, wrists and forearms.
Too hard? Try hanging from the bar with your arms and body completely straight, and increase your hang time each session. When you're able to hang for a minute, make it harder by wearing a weight vest or hang using just one hand for a short period of time before switching hands and alternating back and forth.
-- Nick Anthony, Performance Specialist, Athletes' Performance