Nothing will make your dog want to move away from you more than jerking the leash and dragging him. If your dog lags, be careful not to reinforce this behavior by giving him attention when he stops. Instead, stand still facing away from your dog and put gentle pressure on the leash and wait. Praise your dog if he moves even one inch to come towards you. Alternatively, go to the end of the leash and kneel down facing away from your dog and wait for your dog to come to you, praising him all the way.
It does not matter how long it takes for him to start walking, (although it should not be more than a minute or two), he eventually will. Then, walk another few feet away and repeat if he stops. If your dog is afraid of leash walking, you will need to take him out for numerous confidence building training sessions on leash. You do not want to take him with you on an errand when you may be in a hurry and get frustrated with your dog. Once you have taken the time to teach your dog to enjoy leash walking, he can come along with you on all your errands.