It's common for dogs to yank on their leashes when being walked.  A simple solution is to use a "Gentle Leader" that hooks onto a leash.  Instead of wrapping around the dog's neck it's attached with a nylon strap above the muzzle and behind the ears.  Looking somewhate like a muzzle, it doesn't prevent a dog from opening its mouth unless the leash is pulled.  Tugging forces the dog to turn its head back toward you and tugging harder only makes its head turn more sharply so that the dog stops the behavior eventually.  Also try stopping when your dog tugs on the leash and refuse to move until the dog stops.  In time the dog will modify its behavior.

Hope this helps make your leash walks more enjoyable for both you and your dog.