I have to echo everyone else...treats, treats, treats. I have a distinctive call that I make when I head outside with treats. And I always bring them treats, even if it is just a bit of bread. When they hear the call, they come. The chickens who have been with me longest know the call, and come running everytime they see me. The newer ones are beginning to catch on. I am rarely without bread in my pocket.
I also have a milk carton in the pen that I sit on, and I go into the pen with my morning coffee and at other times of the day just to sit and watch them. They've gotten used to me, and the older ones treat me as one of the family. They'll even stand on my feet, or if I am on the grass, they'll walk over my lap. They are free-range, and so they even come up on the porch and to the door, and this morning, one of the hens literally knocked on the door with her beak! The other day, a hen walked on the dog, who was lying by my feet, to get to a piece of bread. 3 times! I think the key is to be calm yourself, and not too eager. It takes time, and in the meantime, just enjoy watching them interact with each other.