Step 1: Don't be a jerk. I mean it. Just... don't.
Step 2: Practice active listening. This means actually paying attention to what the other person is saying, instead of just waiting for your turn to talk.
Step 3: Use empowering language. Instead of saying "You're so stupid, you'd think you could fly," say "I appreciate your unique perspective on things, even if it's not exactly... accurate."
Step 4: Avoid criticism. This one's a toughie, but trust me, it's worth it. Just pretend you're a therapist, but not that kind of therapist.