By starting your puppy off right, you can expect many years of pleasant walks together. EVERY time your puppy is on a leash, it is an opportunity to teach him what you want. If you are unprepared to teach him he will still learn, but it will be to pull you rather than walk nicely by your side.
Start by using the right equipment. I recommend a 4-6 foot leash. The flexi leashes provide constant tension and can actually encourage pulling. Ask for a "sit" and hook the leash to your puppy’s collar or harness. If you move forward and the leash is tight, the puppy is pulling. Continuing to move forward will teach the puppy that pulling is good. It gets him where he wants to go! Don’t reward pulling. Stop immediately. Wait for the puppy to move to where the leash is slack, then move on. Your walks may be somewhat annoying at first, with all this stopping, but keep it up. It’s a small price to pay for years of nice walking to come.
Encourage your puppy to pay attention to you. When the puppy starts getting the message that a loose leash means he gets to move forward, ask him for more. If the leash gets tight, stop and wait. When the puppy looks back at you, immediately start moving and praise the puppy with a “good dog!” Teaching a puppy to walk on a loose leash and to pay attention to you is well worth the effort. Have patience with your puppy and take the time to do this right. A dog that pulls usually becomes a dog that doesn’t get walked, which can only lead to trouble for the dog and for you. Encourage his attention by turning frequently and by practicing sit randomly while on a walk. Turn it into a game by playing “red light, green light” with your puppy. Red light if he pulls, green light when he sits. Have fun!