My dog is a vicious, aggressive gobshite (mainly due to back pain and poor temperament), but she does walk very nicely on the lead.
When she was 9 weeks old I put a little cat collar on her with a light nylon lead trailing, and let her move around freely with it indoors. I'd leave it on her for increasing periods of time so she could get used to it - couple of minutes, 5 mins, 10 mins etc. Once she could cope with the collar and lead for 10 mins, we practiced indoors with me holding the end of the lead so she got used to being restrained by it.
Once she was handling that happily, we advanced out into the garden and did a couple of minutes walking around together. I was taught to simply walk at a normal pace with the dog, ignoring all the leaping and pulling and puppy antics, until she settled and walked normally for a few moments - then reward and end the session.
By the time she'd had her jabs and we'd done a few sessions like that in the garden, she was walking nicely on a harness, no trouble.
Now, 11 years later, if anyone can give me a foolproof method for stopping her attacking anything that moves that would be great thanks.