Here is an article from Karen Pryor's website (with permission of course!) with excellent Loose Leash Walking (LLW) tips. There is also a brief video and the option to purchase the entire video.
The important messages are:
~Loose Leash Walking is not a natural activity for dogs and must be taught like any other trick
~A dog will pull if it gets them what they want: faster access to the car, a squirrel, or even for their owners to give up on leash walking!
~Allowing a dog to pull even occasionally can be disastrous to LLW training. (I am guilty of this... when I only have a few minutes to get Gilda to Doggy Daycare and she's excited to be there...)
How to Teach Loose-Leash Walking