If you just got him let him get used to his surroundings first before you play with him/her. Treats are a good way for him to learn that your not bad an that he/her should like you. If you had him for a while you can do what I did with our one who was nervous around us we bought a small pets play pen big enough for me and my piggy I got it from walmart and I just sat in it with him and let him sniff me and just get used to me or you can sit in your bath tub on a towel so the bottom is more feet friendly for your piggy and Just sit in it and let him climb you and get used to you that way. Just stay quiet and still when your with him and let him explore your and get used to you.
The guinea pig needs to get use to you and its surroundings. If you keep putting your hand into its cage at the moment he will bite. Simply talk to him everyday so that you can build trust. When you feel comfortable open his cage and let him explore a bit, and come to you. http://www.cavyspirit.com/care.htm
ok,this happened with my cousin's hedgehog.if you ever go jogging or running or even just getting out of the shower,get a washcloth and rub it all over you.put the washcloth in its cage so it will get used to being around your scent.also just let it run around the room for a while to get used to it's surroundings.