As navjot said Do not follow Caesar Milan, it is good for a TV show and not for real life. The dog pulls because you move when he pulls. So he has learnt that he needs to pull you along.
When my dogs pull I will come to an immediate stop. No matter how long it takes, I will stand there like a statue till the dog releases the tension on the leash, at that instant I will praise and move forward. The moment he pulls again, I will stop. This will be a very painful experience for the first week or so, but the dog will learn that pulling this leash will make me stop.
This is the old way of teaching the dog and very inefficient. The scientific way is marker method. Please google marker training.
You can also visit my website www.youtube.com/user/rrnsss
to see 100s of how to training videos including loose leash walking.
Here is how I train my loose leash walking