You know the feeling. You step out the door and before you reach the corner, your arm is already stretched out in front of you. It feels like your dog is leading the walk, and you are mostly following.
Pulling works, so your dog does it
For a dog, the outside world is exciting. Smells, sounds, other dogs. If pulling gets them to all of it faster, they learn on their own that pulling pays off.
"A dog who pulls is not a difficult dog. It is a dog who doesn't know yet that walking calmly gets you somewhere too."
Three things that really make a difference
Stand still the moment the leash goes tight. Only walk on when it relaxes again. It takes patience, but your dog quickly learns that a loose leash opens the way.

Reward the moments beside you. A word, a treat, a touch. And finally, choose gear that helps rather than works against you. A harness with a chest clip gently steers, without pressure on the throat.
What to look for in gear that helps
Not every harness does the same job. Look for a clip at the front of the chest as well as one on the back: when your dog leans into the leash, a front clip turns them gently to the side instead of letting them dig in with their full weight. A harness that sits flat across the chest, with no single strap crossing the throat, also makes a real difference. It should be snug enough that it doesn't twist when your dog turns, but loose enough to slide two fingers underneath comfortably.
A simple routine to practise at home
You don't need a training class to get started. Five minutes in the hallway or the garden is enough. Clip the leash on, take one step, and stop the moment it tightens. Wait for the slack to come back, then take another step. Most dogs work out the pattern within a few short sessions: pulling stops the walk, a loose leash keeps it going. Once that clicks indoors, it tends to carry over outside too, even if the smells make it a little harder to remember at first.
With Nora and Mila, our two Yorkshire terriers, the habit that helped most was standing still the instant the leash tightened, every single time, even on the mornings we were in a hurry. Mila caught on within a few days. Nora, who notices everything that moves, took a couple of weeks and a fair bit of patience from us. Neither of them is a difficult dog. They just needed consistency more than correction.
If you are working on this with a puppy, keep sessions short and expect some walks to go better than others. Older dogs who have pulled for years can also learn to walk on a looser leash. It usually just takes a bit longer, and a bit more patience from you.
Most of all, give it time. Every calm metre is a win. For your dog, and for the two of you.