From ‘The Poloquin Principles’…
""Using this type of progression I was able to increase the Women’s Canadian National Ski Team’s averge number of chinups from 0 to 12 in 11 weeks!
The first progression uses a spotter and starts with hanging from the chinup bar with knees bent. During the ascent, the spotter should support you by holding both ankles. If assistance is needed during this phase, you can extend the leg against the spotters base of support. Once you’re able to perform 12 repetitions in this style with minimal assistance, it’stime to move on to the next progression.
In the second progression the same starting position is used, but this time only one ankle is in the spotters hands- the extra weight of the free leg will increase the overload on the muscles. When 12 repetitions can be performed with minimal assistance, you can move n to the next level.
In the third progression the exercise is performed in the same manner, but this time the spotter will hold you at the waist. as yor strength increases, you will find that you require assistance only in certain parts of the exercise. At these parts of the movements your spotter should offer only enough assistance to help you clear the bar.
When you can perform the full range of movement with no assistance for 12 reps, you are ready to begin using additional weight."
Also, at the end of the progression, it may be useful to perform a few weeks of heavy negative chins (sloooow eccentrics) with a stool under your feet for the concentric part. Hope this helped!