The goal is to NOT let your dog have the reward of moving forward or sniffing as a result of pulling. There are a few ways to accomplish that.
When your dog pulls… immediately stop walking. This is really hard for many people because their dogs are strong. Its also really hard on the shoulders. You can make it easier by making a knot in your leash that you hold in your left hand. As soon as the dog pulls the leash out of your left hand, clasp both of your hands at your core as you stop walking. Wait for your dog to release tension and encourage him to come back to you.
Another option: immediately turn around and walking the other direction when the dog pulls. Here is a good video from local trainer Glenn Massie.
Remember, while on walks, yes or click your dog anytime he is walking nicely at your side. See my other blog post on Tips for Loose Leash Walking.