Just take your dog everywhere you can think of...Petsmart, parks, neighborhoods with other people walking around. If you work in an office with others, taking your dog to work with you, if its allowed, is a great way to socialize your dog around strangers. I did that with my dog when she was a puppy. If there are dog clubs in your area, whether they are GSD clubs or others, its always nice to take your dog there for just a basic obedience class. Lots of other people and dogs are around.