Use slow smooth movements, let them see you approaching from their fronts, don't grab them from over their heads (think spooked chicken and hawk attack)....just common sense things...get down on their level so you are less threatening, be patient, wait for them to approach you, as already mentioned hand feeding is the best one.
If I do put the treat on the ground instead of hand feeding, I scratch around it with my fingers, like a Roo or a Momma Hen offering food. It takes a day or two of doing this. But, eventually they will all come running to you with the scratch sound. Then in another day or two, they will all run squawking to you when you approach the brooder.
Do be careful. It seems my tamest batches of chicks produced the crankiest full grown roosters.