Pyramids, twice a week or so, will help you out alot. For example do sets of 2, 4, 6, 8, 6, 4, 2, or something like that. Increase as you need to as you get better. Right now I feel good about my chinups so I only do them once maybe twice a week to maintain my endurance and my workout is a max set(usually about 20), followed by alternating sets of 8 (2 sets), 6(2 sets), and 5(2 sets), while reversing my grip between those sets. I keep a good pace but at the same time allow some rest between sets. Concentrate on decent form too, although easier said than done when you are wiped. If you do a heavy chinup workout more than 3 days a week, you are overtraining.