A rescue dog cannot tell you what his life was like before you welcomed him into your home. Many rescue dogs are fearful or defensive based on past experience, and a new owner has to take the time to establish confidence and bring out the dog's true personality. Changes in a skittish rescue dog do not come overnight; your patience and consistency will give him a chance to feel comfortable and safe in his new home.
Create a safe haven for your dog. A large dog crate covered with a blanket or towel will give your dog a sense of security and a den-like place to go to when he feels frightened by his new surroundings. If he chooses to spend a lot of time in his crate immediately after you bring him home, do not try to coax him out. If you notice an object in your home that your dog especially fears, remove it if that's possible. If the object cannot be removed, deliberately link sight of the object to a food reward. Create an expectation in the dog that when he sees the object, he will receive a treat. He eventually will associate the thing he once feared with something he can enjoy.
Feed your dog in the same place at the same times every day. Place the food bowl in the chosen place and walk away, allowing your dog to approach the food and eat undisturbed. If necessary, place the food in or near his crate until the feeding schedule is established, then gradually move the bowl farther from the crate until it's at the desired location.
Allow your rescue dog to come to you. A large part of establishing a skittish dog's trust is allowing him to approach you on his own terms. Sit on the floor nearby, but not right next to him. Talk to him in an encouraging way without any sudden movements or yelling. If he approaches you, continue talking to him. Allow him to smell you. If he is calm, slowly offer your hand, palm facing up, for him to smell. Do not pet him until he is comfortable sitting or lying down near you.
Enroll in obedience classes once your dog has acclimated to daily life at home. If possible, hire a trainer to come to your home and work with you privately, so your dog can feel comfortable because he's in his own environment. A group-training class is an effective way to socialize your dog in a controlled environment. He will be able to focus on your cues while becoming accustomed to new people, dogs and environments.