First off, there are a lot of different pull-up programs out. It’s free information and the only difficulty you’ll have in starting a program is discovering the difficulty in picking out which program you are going to follow. Below are a few links to give you an idea of what I am talking about.
I remember a while back in my days at globo-gyms, walking up to the pull-up bar, hitting 3 or 4 strict pull-ups, and think to myself, “This sucks!” and I would then stop.
It’s not that I was thinking pull-ups suck; it’s that I sucked at them and I had no plan on how to get better at them. Not having a plan on how to attack pull-ups and then doing them on occasion was the reason I was terrible at them.