As others have already said, patience, move slowly and speak gently. Our cat was a feral kitten. I'm assuming that her mother was killed. She showed up when she was about 4 weeks old. She was sleeping in our chicken's pen, curled up in their food dish! Their run was a dog pen, so she had walked through the chain link. They were all standing around the food dish in a circle, staring at her. (The hatchery had sent a bunch of cockerels for warmth, that we weren't expecting, so we had to set up some temporary quarters.)
At first, she would run off and not come to the food until I had been back inside the house for some time. Eventually, she would watch me from the wood line. Then, she let me watch from a distance as she ate. That distance got shorter and shorter. By the end of 2 weeks, she would even come over by us as we sat in the grass, but we still couldn't touch her. I also set up a bed for her, so she would have a warm place to sleep.
My DH would move his hand in the grass, to play with her and I could see her eyes light up, but she wouldn't come closer. Kittens have a really strong play drive. I went to the store and got one of those cat toys with leather strips at the end of a long stick. Any of those types of toys would do. I figured that she wanted to play, she just needed the toy to be farther away from us, so that it would be less threatening.
It worked great! Within 2 days, she was so excited in her playtime that she didn't even notice how close my husband's hand was getting to her and when he touched her, she didn't even mind. By then, she associated us with food, a warm bed and fun. Gracie has turned out to be the nicest cat. She is very affectionate and sweet, a real lap cat. Our vets have said that she is a pleasure to have in the office and the nicest cat in their practice.
Good luck with your kitty!