Although most dogs are lovable, friendly beings that approach you rather than the other way around, dog personalities are as varied as our own and inevitably there will always be the reluctant, shy loner.
If your dog has difficulty letting you or others touch him, watch this handy video for training them to be more confident using a clicker.
Warning: This exercise needs to be taken seriously, as if done wrong you can scare a dog, and a frightened dog will bite, as will any animal that is frightened.
If you are worried that your dog is too shy or frightened to work with, you can talk to an animal behaviorist first. Another game you can do is just tossing the dog treats, and feeding the dog his meals by dropping the kibble for the dog following you.