It’s good to make a distinction between walking and heeling. A heeling dog should be actively paying attention to you, while a walking dog can sniff and roam a little.
Active physical games are wonderful for training. Enforce some ground rules and take frequent breaks, using the continuation of the game as a reward for obedience training.
Keep your dog secured on a leash and ignore everything they do. If they sit and look at you, give them a treat. Soon you’ll have a much more attentive dog
A dog’s brain is very context-dependent. You have to teach them Sit From Down as well as Sit From Stand. In the dog’s mind, they’re entirely different. Use at least three positions to keep them listening.
Before you attempt on-Leash heeling, make sure you can heel your dog off-leash. Otherwise you’ll use the leach for physical control, and it will become a permanent crutch
Hollow chewtoys can be stuffed with food, making them very interesting to your dogs. Your dog is going to chew, so you should show them what you want them to chew.