Let the speaker know you are listening and understanding-give encouraging signals like smiling or nodding.
Speak in the group-not at them. People who speak at a group leave no space for response and tend to dominate. People who speak in a group consider the other members. So:
Make contribution, but don't dominate.
Ask question,but not too many.
Speak to the whole group-not just to your friends.
Acknowledge your errors and apologise,"oh i see, i'm sorry i misunderstood"