As centrarchid said, the secret is to relax and not to force anything, or even think about forcing anything. Have you ever had anything to do with horses? You need to completely forget/not think about patting them or touching them or doing anything. When you stop "trying" they will stop being so scared of you.
I have to agree with this approach when you have lots of chickens. I bought all my chicks this spring over a 3 week period and currently have a flock of 20. There was no way I could hold and tame them all so I just didn't even try.
Out of the 20, about 7 are now very friendly and want to be around me. My thought process was to just take good care of them and since trying to pet or pick them up terrified them early on, I just started ignoring them. Eventually, when they were allowed out to free range, is when some of them started to warm up to me.
It's now to the point that the friendly ones actually pester me to interact with them. When I'm sitting out on the patio, they will scare the heck out of me by jumping up on the back of the chair and start chattering. A few of them will climb in my lap and just sit with me or stand on my lap and use me like vantage point to survey the landscape.
Amazingly, just yesterday, one of the lowest hens in the pecking order and one that has never let me get within 6 feet of her, jumped in my lap. Blew my mind!! I think she finally got over her fear of me by seeing the other ones jumping up and sitting on my lap and chattering away.
I've come to the conclusion that just ignoring them gives them time to work through their fear issues and since I'm not forcing myself on them by grabbing or chasing them, they must no longer consider me a threat and probably they view me as more of a curiosity, not to mention the provider of yummy treats!
Maybe at some point, and given enough time, they will all eventually come around and become friendlier. But then again, I'm not sure I want 20 chickens hanging with me when I'm relaxing on the patio because I actually don't want them on the patio!