Loose Leash Walking - Pt 1
If your dog pulls on the leash when walking, it is probably because it has discovered a behaviour that is rewarding.
Perhaps it pulls because it wants to get to the park (or alternatively back home for dinner) more quickly. And it has learnt that if it drags you along behind, then yes, it does get to the park / home for dinner more quickly! Another dog might pull because it wants to go sniff the p-mail left by other dogs, or to sniff another dog's rear end. Yet others might want to go chase a cat / squirrel.
There are several techniques you can try to change this behaviour, depending upon the size and age of the dog; the size and age of the handler; and the environment where you walk your dog.
Be a Tree
This is where you should start with leash training a young puppy.
Quite simply, if s/he pulls on the leash, trying to gallop off in a particular direction you should stop dead in your tracks, rooted to the spot (Be a Tree) - but with a young puppies do make sure you don't jerk their neck as that could cause them injury. You shouldn't tug on the leash at all. Just put it on the puppy, use a treat or toy as a lure to encourage it to walk with you, giving the command 'Heel' or similar, and then reward the pup when it moves appropriately. If its attention wanders and it tries to gallop off, simply stay where you are, rooted to the spot. The pup will look around to see why it cannot move, so call him to you, reward to reinforce the behaviour, then encourage the pup again to walk in the direction you choose, and reward appropriately, and frequently.
If you tend to walk your dog whilst talking on your 'phone; texting; browsing etc your dog will quickly realise that your attention is elsewhere and make his own amusement. Your attention should be on him unless you are in an environment where it is safe to leave him to potter on his own. Once you have put your 'phone etc away and are focussed on your dog, call him in to heel if he starts to rush ahead, or lunge to the side. 'Be A Tree' if you have to and don't move off until he is sitting at your side. If he continues to pull, you need to 'Be Unpredictable' so that he has to watch to see what is happening next. Take maybe 6 or 8 steps in one direction, call your dog in to heel, then abruptly about turn and take 10 or 12 steps in the opposite direction. Again, give the dog the command to heel close, and again about turn abruptly, walking back in the original direction. Vary the number of steps back and forwards, and your dog will quickly become confused and focus on you to see what is happening next. You can throw in some stops with sit-stays, or down-stays, or a circle of your dog... Anything that is slightly different to get him used to focussing on you once again - and you on him.