It is more difficult with dogs that have already learned that pulling is rewarding (eg. get them where they want to get quicker, which is why they pull in the first place!) but I teach mine not to pull by simply stopping when the lead goes tight, and walking on again when the lead goes slack. You have to be 100% consistent, (if you carry on walking even once you are reinforcing the behaviour) but it works effectively.

You might need to help your dog correct itself at first, by moving him/her to your side when you stop, but they soon get the idea. Our 7 month old pup was almost pulling over my 6ft husband when she came back to us, and the pulling was constant, even if she was choking herself, but I can now walk her with other dogs and a pushchair. She will occasionally take a little pull, but as soon as I stop, she turns her head to loosen the lead and we carry on.

I have only ever had her in a flat collar, although the people we got her back from used a harness.