Have an alternative activity if the one you try does not engage students as you anticipated. This does not mean that if a discussion does not heat up immediately you should ditch it and revert to lecture. Students need to practice discussion activities a few times before they become proficient at them. Hang in there with them as they learn to discuss easily and well. In one study, instructors waited on average 0.9 seconds before calling on a student or answering their own questions.
Silence is an important factor to be in control of in the classroom.
Americans are uncomfortable with silence and 10 seconds can seem like an hour. We recommend that you count to yourself while you are waiting for students to answer a question. Few students can come up with any answer in 0.9 seconds, and in our culture, white males are much more likely to be the ones who do. To give women and minorities a chance, push yourself to allow for some silence. At worst, if the silence drags on for too long, some student is sure to answer if only to come to your rescue.