Many people make a common mistake when leash training a puppy. They think that all they need to do is snap a lead on their pup and away they'll go!
The problem is, a dog does not see leash training as being that cut and dry! Until they learn otherwise, they believe this is some type of torture device!
When you first introduce your puppy to leash training, put a lightweight lead on him and allow him to drag it around the house, without you even attempting to guide him with it.
Some dogs will get very upset about this, but if you ignore them, they will eventually resume their play and forget that they are dragging it.
If your dog decides to chew on it, divert his attention to a different toy, but other than that, do not act as if you even notice the leash.
Once he is comfortable with dragging it around, pick up the end of the lead, but allow the pup to have the full reach of it, without you trying to reign him in.
If he sits down and refuses to move, simply have a toy in your hand that he can see, but not reach.
Offer him the toy, making sure that he has to move towards the toy in order to have it.
After doing this a few times, he will no longer be afraid to move while you are holding the end of the lead.
Other dogs will start screaming, fighting, and pulling as hard as they can to try and get away from it.
In this case, keep a hold of the leash, but then ignore your dog's reaction. He will settle down on his own, although it may take a couple of minutes, which will seem like an eternity!
Do not speak to him while he is doing this, just patiently wait him out.
Once he has quit struggling, then follow the same procedure that you would for the pup that refuses to move.
Always end your leash training session with a positive experience. After you have loosely walked your pup, drop the lead and allow him to drag it again before you take it off of him.
Usually leash training a dog only takes a couple of days and he will quickly look forward to it, if you reward him by taking him to new areas to explore, while he is on it.