Having your dog Walk to Heel will make your life so much nicer and calmer when it comes to days out and the daily walk. Not only will you enjoy those walks so much more so will your dog.
Dogs that pull are not in control and havent been taught to walk nicely by their owners, this can cause over-excitement or anxiety when it comes to walking and creates other behavioural issues when meeting other dogs or people when out walking. 
I have gone through a few of the better techniques and I would always use a slip lead and collar when training the dog to walk nicely. Harnesses encourage a dog to pull and are generally not recommended