Somewhere between four and eight months of age, your puppy will gain a substantial amount of size and strength. If you haven't taught him the basics of walking nicely on a leash by this time, he's likely walking you. If you adopted an adult dog, he may or may not have had experience on a leash. An adult dog can pull exceptionally hard, making him difficult to control.
One way to work with a puppy or an adult dog that pulls is to reverse or change direction suddenly without saying anything. Your neighbors will likely think you are nuts for walking in bizarre patterns; however, your shepherd will learn that if he pulls and isn't paying attention, he'll feel a tug on the leash and have to catch up with you.
Using a head collar allows anyone to be able to walk a strong adult shepherd with pulling tendencies. With this collar, as soon as the dog pulls, his body whips around to follow his head, causing him to stop. He quickly learns that pulling doesn't move him forward.
Additionally, while working with your shepherd on good leash manners, always reward good behavior. Whenever he is in a good position, click and reward. If you want precision heeling from your shepherd, you will continue to refine this position while walking straight ahead for short distances (such as ten yards). The variables to increase will be distance and direction. Remember to introduce variables one at a time and in small increments.