Here's a heresy: "How do you know that?" is a powerful question for helping people think, but it's not the best question. The best question is, "How … - Peter Boghossian

Know when to walk away, even when the conversation is going well. Putting pressure on your partner to continue a discussion beyond their comfort level shuts down listening, encourages defensiveness, and turns the conversation into a frustrated rehearsal of why one of you is correct and the other dense.

Give faith-based justifications no countenance. [...] Let the utterer know that faith is not an acceptable basis from which to draw a conclusion that can be relied upon.

Seemingly impossible conversations typically have one thing in common: they're about moral beliefs rooted in one's sense of identity, but they play out on the level of facts (or assertions, name-calling, grandstanding, threats, etc.). [...] The most difficult conversations, then, masquerade as discussions about something other than morality, but they are actually about what qualities, beliefs, attitudes, and behaviors individuals believe make them good people or bad people and why it is important to hold the right views among those.