The best training for one arm chins (assuming you are not able to do any as yet)usually happens in several stages. First, hang from the bar with one arm. Do two sets at the end of your regular training session. Don’t rush this period take at least four weeks.
Next, take an underhand grip (Chin-up fashion)and from the top position (get a bench to stand on)lower yourself as slowly as you can with one arm, this will not be easy. Do two of these negatives at the end of each training session. Do this for four to six weeks.
Next, grap the bar with a Chin-up grip. The free hand should be placed on your wrist that is holding the bar. Perform as many Chins in good form as possible. Do only two or three sets as you work these into your regular Chinning routine. Do this for an additional six weeks.
Next, begin to lower your hand down your arm. You began by holding your wrist, now grab your your forearm, or lower if possible. Perform three sets in this manner. This stage should last about four to six weeks as well.
Next, work your hand down your arm grabbing the bicep and performing as many reps as possible, three sets. Again, don’t rush take another four weeks or so here.
Eventually, you must remove your hand from your other arm. Some people can now perform a one armed Chin-up, some still cannot. For those still having a difficult time I recommend hanging a rope, or towel off the bar and holding it at as low a level as you can in order to Chin yourself. This stage could also last up to six weeks or so.
Eventually, you will be able to perform the one arm Chin. Other than the obvious body weight to strength ratio needed to perform this movement, you also need balance. Your body is not used to working in this way and it will fight to achieve the balance that it needs. To that end it is a matter of getting used to the movement.
If you have low body fat, high strength levels, train this movement three times per week and take the proper rest periods after a six week session you should be able to perform this movement in under one year.
Make sure that you cut back some on your normal Chinning routine. Also, train both arms equally!