Lots of trainers have lots of different methods to stop dogs from pulling on the leash.

Method 1:

When your dog starts pulling on the leash, stop walking and hold the leash tight until your dog gives slack by turning around or to the side.  Once your dog has given up on pulling, you may start your walk again.  Chances are, she will immediately start to pull and you will have to immediately stop again, and again, wait until your dog stops pulling and turns around or to the side, giving slack in the leash.  This will take lots of time and patience and does not have a 100% probability of working long-term.

Method 2:

When your dog starts pulling on the leash, stop and turn her around saying “let’s go” and walk in the other direction.  Most likely, she will again head to the front and pull on the leash.  Again, stop and turn around saying “let’s go” and walk until she pulls again.  You get the picture – it will take many, potentially, hundreds of “let’s go’s” to send the message to your dog that pulling will not be tolerated.  Eventually, most dogs will get it and begin to watch you for their signal to continue or turn around.  Only then can you walk consistently on a loose leash.

Method 3:

Now we are getting into hardware – collars.  If the above methods do not work, or you prefer to skip ahead to a quick fix, here is your solution – at least 90 percent of the time.  The gentle leader, or halti, is a collar that has a muzzle loop in addition to a standard flat collar.  The muzzle loop is where all the magic happens – the leash connects to a ring that is connected to a strap which connects to the muzzle loop.  It does not connect to the flat collar at all.  As such, when your dog tries to pull you forward, you can, with slight leash pressure, move his muzzle, and therefore his entire head, to the side.  When this happens, he will stop walking or slow his walk in an attempt to stop the uncomfortable pull to the side.  But the process takes time – at first, your dog will fight the collar/muzzle loop with all she’s got – she will look like a bucking bronco at times, but most of the time they will be using their paws to try and push the muzzle loop off their snout.  It often takes several walks for them to get comfortable with the halti, but they almost always get to the point where they realize there is no way to get it off and become tolerant to the device.  Once that happens, walks become an enjoyable time as you walk in harmony on a loose leash.

To facilitate getting your dog accustomed to the halti, you can use treats, lots of them.  When you first put the loop over her snout, give her treats.  Once it is fully clipped on, give her treats.  Before you start walking, put the halti on in the house for 15 minutes at a time, giving her treats from time to time.  After a while, she will get a little more accustomed to having the contraption on. When you start walking, give her treats. 

Method 4:

The infamous prong collar.  It looks like an archaic pain device used in the Middle Ages.  There is much controversy over its use, even among positive dog trainers.  Some believe it creates excessive pain, others believe it only gives a pinch that is at most uncomfortable.  If you choose to use it, here is how.  First, I would only use a Herm Sprenger brand prong collar.  This collar has very dull prongs but they are shaped in such a way that they still provide the necessary pinch to the dogs neck if he pulls hard.  If your dog does not pull hard, or is just walking on a loose leash, they will feel nothing.  The collar should be a couple of inches larger than the dog’s neck.  You can remove the prongs one at a time, making the collar smaller and getting the right fit, which is tight enough to do the job but loose enough to fit a finger between the end of the prong and the dog’s neck. 

Once you have the collar fitted properly, connect the leash, and start walking.  When your dog pulls, do not apply backward pressure.  Instead, “pop” the leash with medium strength such that the prongs pinch the dog’s neck and make him uncomfortable.  He will naturally turn to see what’s going on and when he does, he will slow down and the pressure will be released.  He will learn quickly that moving ahead of you is uncomfortable and walking alongside you is preferrable.