This video on loose leash walking was put together by an agility instructor but it is almost exactly the same way I teach loose leash walking, when using a flat collar, for our urban dogs. It’s a great video and a brilliant way to work on attention on leash. Even if you use another walking tool, you should give it a watch.
Remember that we deal with many more distractions that most dog owners, so for this exercise your rewards may need to be very high value. Do not expect the same result as this trainer gets in 15 minutes. She is not dealing with other dogs, kids, pee smells, grocery stands, etc. all within the same sidewalk. Your job is much harder than the average trainer!