Start out on an assisted dip/chin-up machine. When I started lifting heavy last year, I couldn't do any chin-ups, or dips. I stopped doing chin-ups for some reason, but kept with the dips.
I started out on the assisted machine. I did 4x12 on a weight that I struggled to get all 12 in. Each week, I would decrease the weight on the dip machine by 5 lbs until I got to be able to natural dips. Over the course of about 8 months, I went from not being able to do any dips, to being able to do 12 dips with a 45 lb plate strapped to my waist. So hopefully I'll be able to do the same thing with my chin-ups. Hope this helps.