By having prayer requests taken seriously Ideally a member who misses a meeting will be called by the leader and others. Everyone matters in a group and we miss anyone who isn't present. This will also give opportunities for encouragement and service if there is a problem or obstacle to be overcome. While the focus of the group is upward, it is still healthy to take a look inward now and then. Look at establishing goals, and informally measuring the common progress in meeting them.
Some groups establish a covenant which lists the expectations of the group.
The expectations should look two ways. The group needs to know what it is expected of the leader, the content, and the opportunities for growth. At the same time the individual needs to know what is expected on him. It is best if these and other questions are discussed before they are a problem rather than after. The leader of the group has an important job.