This post is ostensibly about how to speak to children (and is a good list for that). But it also seems like a great list of tips for speaking to people, of any age. Particularly:

• Make eye contact
• Keep it simple
• Use requests instead of demands
• Don’t escalate your voice if/as the other person escalates theirs
• Ask the right questions
• Give alternatives
• Speak in “can"s instead of “can’t"s (can’t is a “challenge accepted” trigger)