Hi diane4! You might want to visit the article on Dog Obedience Advice about
How to Stop Dog Pulling On the Leash
I also read somewhere about the tree method. What you do is that when your dog applies any tension on the leash, you stop and be a tree (be immobile). When you feel the leash slacken, encourage the dog to go into the heel position and then praise your dog. A treat to go a long the praise will also be nice.
The key is to stand still whenever you feel the tension or if the dog is about to apply tension on the leash. Be consistent and I'm sure your walks will be more pleasant.