The above exercise works well for young puppies and is a good method. I would like to also suggest : 1. Yorkies and other toy breeds should have a short regular leash, hooked to a halter. Never hook a leash to their neck collar. Do not use a flex-leash or long leash for training.
2. With the dog sitting on your left, pat your left knee and Give the CUE word 'HEEL', start off with your left foot. (Heel is different than a free will walk. Heel means stay right by my leg and pay attention to me, we are working now.) I do not teach that dogs must heel all the time. But they
must heel when cued to heel, until released with Sniff Around. Several times on a walk, I release with Sniff Around and allow them to sniff, potty and explore. Then I cue them with Heel and pat my left knee. to resume our walk.
3.The reason dogs surge ahead is because they are
Not Watching You, They are not following a leader, they are checking doggie mail (who left pee or poo messages) and looking for adventure. A cat to chase, other dogs to meet, candy bar wrappers and so on. You must teach your dog to follow you. Teach your dog to heel in the house first. You teach this like any other lesson, once they can obey and understand in the the house and your own yard, then you move the training outside where there are distractions.
4. There is a difference in teaching your dog to heel and Correcting him when he doesn't heel. If a dog bolts you can say NO firmly and stop in your tracks. Eventually the dog will realize you are not coming and will come back to you, to see why you are not following him. After awhile he will understand, that you have to walk together. That you will stop if he gets in front.
Another way to correct is as soon as he runs in front, Say NO and make a sharp turn going the opposite direction. This does make him to keep an eye on you and does tell the dog, I am leading you. But it is still correcting.
5. There are different exercises you can use to train your dog to look at you, for leadership and direction. I hope this helps.