Loose leash walking on a flat collar is a trained behavior and takes time to achieve. While it's a wonderful goal to work toward, you often have to manage situations with other walking devices depending on your dog’s size, strength, and comfort.
Front-clipping harnesses, in which the leash attaches at the dog’s chest, are great for dogs of any size. Head halters, which attach under the chin, work great for stronger dogs. These devices provide extra control by creating pivot points that redirect the dog from the attractive thing they’re pulling toward. Keep your dog close to you when moving through crowds and other dense public places.
Create a positive association and introduction to the device you choose by letting the dog wear the device inside for short periods and providing food rewards when the dog is calmly wearing it.