When I teach adults beginners, I always start slow and build my way up through several stages. First, I just get them to mark a piece of paper in response to my questions, just to see how much they really understand. Second, I get them to repeat answers out loud as a whole class. This gets them used to speaking out, even the very shy ones. Then I ask individual students to repeat out loud, starting with the better students, but giving all students the chance to speak. Then I get them to answer simple questions with only "yes" or "no". Once they get used to responding with one word, I ask them to respond with two words, then three or more. This progression has always worked well for me.
As for specific activities, with beginners I use dictations and basic Q and A techniques mostly. As they progress, they can work on debate or giving short presentations, but that takes time.