Keep him on a short leash, and pull him back if he tries to drag you. Carry some treats in your pocket to give to him when he stays beside you. It's important to show him that you are the boss, not him. Once he knows that you are the alpha dog, he will obey you more quickly.
You have to teach him command "heel". Taking lessons is a good way. You may need better equipment, too. When he walks ahead, simply turn around and walk in other direction. Say "heel" and when he comes back, praise. Takes lots of patience.
There is a harness called the Gentle Leader. When the dog pulls it causes the dog to turn around and look at you which means you now can get the dogs attention and correct the behavior. Also start with the dog in a sitting position, and take a couple of steps and then make the dog sit again. Keep adding a few steps between sits, and then just so the sit when the dog starts to get out of position, don't wait for the dog to pull to make it sit. It takes time and consistency.