Start small and work up.
I'm currently going over everyhting with Buster.
For instance "focus" (look at me) I started int eh hosue alone, then in the backyard alone, then with the other dogs around, then on the nature strip with no one else around, now we practice it when passing cars, trains, kids or sometimes, people.
Eventuallyt he aim is that he will pass other dogs without reacting, but there isn't enough in it for him atm. The reward of reacting at the dog is bigger than looking at me.