To involve students actively in the process of learning, i often give them tasks to do before starting a new unit.
For example, before starting a unit tackling the theme of environment, students in pairs should look for pictures, proverbs, quotations... and give a short talk about the topic before their mates.
With my students, we started this unit of environment on a somewhat pessimistic mood. Our moto was: one picture, one problem, a short talk. Students did the task willingly, and ALL of them found telling pictures about air pollution, garbage, fumes..., and did quite a great job.
I was really surprised at my students' performances.
Let's give our students the chance to speak, to venture and to gain.
"Nothing ventured, nothing gained"