Kikopup's LLW Video
I primarily use this method + changing direction when I have to. I find adding the clicker to the changing direction method makes it go MUCH faster, although I am adamant about NOT clicking the dog for returning to you, but ONLY clicking when you are actually walking and she's walking with a loose leash. If you click immediately when the dog returns to you, rather than after you take a step or two, some dogs turn into yo-yo's- go out pull, come back for treat, go out pull, come back for treat...
Another trick I used is I change direction while the dog is
on his way to pulling, but before the leash is actually tight. When you see the dog's nose pass an imaginary line a few inches in front of your toes (maybe 6-12 inches for a Newf), you can change direction.
Pay attention to clicking a true loose leash, when the bolt clip is hanging straight down. Nothing else will cut it. If you are specific with that, the dog learns to notice much more subtle pressure than if you click anything else.
This page also has a really good LLW description, about halfway down under "LEASH"
Sue Ailsby's Training Levels
And ditto what Jackie said, behavior that's rewarded sometimes becomes very strong. You have to notice little things like the dog pulls to sniff something and you let them sniff because you were going to anyways (I'm guilty of that and trying to be more diligent), LLWing all the way up to something good (like a person or dog) and pulling the last few steps. Those last few steps turn into the last several steps...
The little stuff like that can be a pain in the butt.