As instructors we need to teach (and model) the behaviors we want to see. With regard to radio discipline, make it a habit to immediately cease ALL conversation the moment you hear anyone talking on the radio. Even if that means stopping in the middle of a word. Talkative passengers in busy airspace? Explain before the engine starts the ‘Sterile Cockpit’ concept and if they do not comply, that you will be making extensive use of the ISO switch before returning to the airport to drop them off from their last flight with you.