Dogs that are shy or wary of strangers have either had a bad experience with people or weren’t well socialized as puppies.  Only positive experiences can build up their confidence.  If your dog is one of these shy types, you’ll need a good strategy and lots of patience.  Arrange to meet a friend when you’re out with your dog. Ask the person to stop and chat but ignore the dog.  Don’t talk or even look at him.  Wait until you see your dog is relaxed, them give him a dog treat then go on your way. Repeat this exercise often with that friend and others until your dog no longer tenses up in their company.  The trick is to notice when your dog relaxes. That’s when you can praise him, pet him and offer treats maybe even buy him a new dog toy. In time, he’ll enjoy the challenge of meeting new people.