Start in a less distracting environment -- not a busy street or a trail with lots of wildlife. I prefer either a front clip harness or a flat collar on walks with my dog.
Decide what criteria you want for loose leash walking -- do you want a perfect heel right by your side or do you just want your dog not to pull on the leash but don't really care what position they are in?
Start walking. If your dog pulls, stop walking. Pulling is a self-rewarding behavior, so removing that "reward" will help them realize that they have to walk nicely to get where they want to go.
Alternatively, if your dog keeps pulling forward even when you stop, turn around and walk the other direction. You can say "let's go" or something similar to get their attention if you need to.
These steps might look a little silly at first because you probably won't make it very far forward very quickly, but after a couple sessions, most dogs start to understand. The most important thing with this skill is consistency! You can't let your dog pull sometimes but not others. Stick to the same plan, and you will thank yourself later!
Once your dog is solid with loose leash walking in a quiet environment, slowly start to work on it in more distracting places. You may have to go back a few steps since they might forget everything they just learned as soon as they see a squirrel or smell something yummy (like crunchy leaves in the fall).
