In a large group, most students are content to sit, listen or pretend they are listening and wait for somebody else to participate. To avoid this, I make them work in small groups. Besides, being in a small group can make the activity less intimidating for them. You can also try pair-work. In pair-work activities, each student gets more speaking time, students are much less embarrassed about speaking, fluency improves and they make the class atmosphere nicer and more natural.
