I used bread. It's easy to break into little pieces, and cheap and easy to find! It's a very special treat so it's a big deal. In fact, I made a game out of it that cracks my children up...I go outside with the bread partially hidden in my hands and say, "Who loves me??" And the ones that immediately come running, get the bread. The others miss out. That started even the unfriendliest ones scrambling to be first!
The ones that run up, but don't want to eat out of my hands, I just toss it a little ways away from me. Still within grabbing distance (but I don't grab) and the ones that eat out of my hands, of course get more. Not all of my chickens like to be picked up, but a lot of them do like to be petted.
Sometimes just a stroke down the back, like you would a dog or cat. Other ones, fly up on my lap or shoulder and want their wattles and the skin around their eyes rubbed. Very few of mine want their heads scratched.
Don't be discouraged...out of about 12 chickens I raised from babies, only about 5 will actually climb up and want to be held. None of my guineas will let you really touch them, and won't eat out of our hands, and then the 2 geese, who will let you pet them, but not pick them up.
Obviously the #1 way to get their attention and affection is food. After that, it's just up to the chicken. Oh, and don't forget there is the "teenage" period where even the tamest bird thinks you're going to eat it!
They grow out of that, though!
Good luck!
Shelly