When I was teaching critical thinking a major part of the students grade was a group project.  This being the case I wanted to start building a community in the classroom as soon as possible.

On the first day I would hand out playing cards to the students and tell them to find the person who had the same card as they did.  This forced everyone to get up and interact by asking each other what card they had.  Then when they had found their partner they were to interview each other with questions I had given them.  Each interviewer was to turn in the responses they had received for their first grade.

I found this technique very helpful for preparing students for the group work activities.