Only study in a public area like a cafeteria if the group members are able to keep focused. Do find a place with comfortable chairs. Also, you may want a room with a blackboard. There are 4 study rooms in the basement and 5 on the second floor. If your group begins to deteriorate into merely a social group, use a strict agenda and a strong convener.
Many groups report that most of their time wasting occurs during late night sessions.
Decide ahead of time when you will stop studying for the evening. Also, to stay focused, schedule regular breaks. Don't allow group members to attend unprepared. To keep members who are failing to do their fair share is to enable and encourage irresponsibility. Remember, you are not providing free tutoring.