Feedback discussions are wonderful for making this happen. Make your students responsible for bringing good issues for discussion to class. Respond in a way that indicates that you heard and understood the question or the comment. Validate questions by either expanding on or challenging them, and encourage students to challenge you . Allow enough time for discussion.
Good discussions take some time for warm-up, reflection, and maximum input.
Give students time to respond. A few seconds can feel like a century, but students need that time to process the question. Warm up your audience. Use review questions from the last session or even a non-related current event to get people in the mood. Sometimes controversial events or issues will jump-start a discussion.