The one most important thing you will want to keep in mind with this command is, you have to make yourself more interesting than anything else around you during your walks. Give your dog a reason to stay with you, talk to him, give him a "sit" command, stop, make him lie down for one second, make it an interesting walk. The most common reason for dogs forging ahead of their owner is they become bored, or their owner allows them to smell at everything along the way, so before you know it "Rover" is pulling you along wherever he wishes to go. Without realizing it, the owner is also allowing "Rover" to be in charge of his own destiny.
You should begin your walk by telling your dog "Heel." Use his name first to get his attention and be very enthusiastic as you give the command. Now, do not forget to talk to him so he pays attention to you, praise him when he is in the correct heel position, which is dog on your left, his right shoulder should be in line with your left hip. If he forges ahead, stop, make him sit, resume your walk and repeat the "sit" as needed.
If your dog insists on pulling ahead, work with him in small counter-clockwise circles. This will encourage him to pay attention to you as you are walking. Do not let him smell the ground as you walk - this will encourage him to not pay any attention to you. Play with him in your backyard and allow him to burn off some excess energy before you try to take him out for a controlled walk (somewhat like allowing children recess at school before class). Another bad habit to allow while walking your dog is eliminating wherever he chooses. You should only allow him to eliminate in a specific area of your backyard. By allowing him to just eliminate anywhere, some dogs will turn this into a "marking" behavior, therefore claiming the entire neighborhood. Your dog's new job is to mark everywhere he can pick up the scent of a strange dog. This type of behavior is also known as a "leader" behavior which is allowing him to have that feeling of being in charge, and could also lead to "territorial" behavior.