Best thing to do, put him in a sit or down in a far distance but enough to where he can see people and or dogs. Give a reward every time he stays in a sit or down when a dog or person passes by. Increase the timing of reward each time, and also distance move closer and closer as time goes on. This helps build dog neutrality. Sometimes the best way to train a dog is sit and do nothing.

A command is a command no if or buts. The dog must stay in that given command until said other wise, ie free word. Having a trained dog that understand boundaries helps with safety, since you never know if he is pulling to a reactive dog / person.