Treats, treats, treats! Make everything he does an enjoyable experience. If he comes up to you on his own, treat him. If he plays with toys, treat him.. etc. Once he gets comfortable around the house, you need to let him experience everything he can so that he can socialize. Walk him, take him to the park, take him to Petsmart. Don't do it too quickly though or you will overwhelm him.
That's really the only thing I can think of. ANY dogs, but particularly rescues will have trouble adjusting to a forever home. I am involved in rescue but I am not able to foster so I'm afraid I cannot provide as much information as a foster mom might be able to. We have a rescue of sorts but she's always been the perfect dog..
However, I can say that it takes a lot of time, love, and patience. He has never known anything like this and I'm sure you can understand why he is hesitant to trust you. He will come around eventually - it may take many more months but he will eventually come around. And how lucky you will be when he does come around. Rescue dogs are so special! You are blessed.
