I disagree with several points raised on here
Harnesses do not teach a dog to pull - some harnesses are safe for a dog to pull in eg canix cross or tracking harness - they will be different to a dog walking harness
Lez Graham is very dominant based training.
The turning around or stopping method can cause a lot of frustration to the dog and the owner! If it worked for you you have more patience than me
Hence it tends to take ages to see a big difference and as the owner gets frustrated they let the dog pull for a bit and then go back to turn around or wait etc so quite inconsistent training for the dog.
Have your dog off lead.
If you start at home indoors and literally have your dog at your side and treat in the position you want the dog to be in. Initially treat continuously and take a few steps and stop. Use the dogs food allowance for this.
For a while always treat at the side of you rather than in front of you. We treat with the dog looking at us a lot. Now treat at the side in heel position.
Make the side position a good place to be.
When the dog is happily aware that treats will come from the side you can then go into the garden and take a few steps and treat at your side.
Do not be tempted to move your hand forward if your dog moves forward say nothing just show the treat and get them to come back to position to get the treat.
Over time you can take more steps and less treats. When the dog is happily coming back to position for the treat then you can add in a word eg "heel" "with me" use a different word to one you have used previously.
When the dog is doing this happily you can then do a fewsteps outside using the word. It may only be 5 steps. Do this on the way back from a walk when you are more likely to get success. Over time build up the length of time you do this and decrease the treats.
It will take a coupe of weeks to get the behaviour and word connection.
In high distraction areas you will need to increase the treats flow but in low distraction areas you can lessen the treats. Over time you will need no need for treats regularly but it is still worth treating on occasion.
If you have the luxury of walking the dog off lead whilst training this that is great if not just make sure you do not use the new word whilst the dog is pulling