The traditional way these marvellous working dog collars are used by professional trainers is to give a sharp jerk—strong enough to make the dog stop what it's doing and do something else. For instance, if the dog starts to sniff and pull on a walk, you quickly brace yourself and give a quick yank in the hopes that the dog feels it enough to stop pulling. My first trainer told us to generate enough strength by actually running full speed in the opposite direction so that my, then 76 pound boxer, would feel a strong enough pop! The next trainer I had taught me to first attach the leash to a fence so that I could practice the technique and get it right before I tried it on the dog. The technique was a lot like karate where you have to twist your hip to get enough power for your body and so that you can get the timing of the correction right. Most trainers do not give owners practice on a fence first. They just let owners make a lot of mistakes on the dog.
So there you have it, an overview of a variety of common collars and harnesses. None is perfect. They are all just tools. But some are more likely to cause problems in your pet or may just provide a less than ideal match for your needs. In case you're wondering which I prefer—ideally my dog can walk on leash with the flat collar he wears regularly. But for those dogs that tend to pull and need more work, I tend to recommend a front-attaching harness or a head collar of some sort.