Remember that everyone is strapped for time. If you cannot attend a meeting, make sure the other group members know that you will not be there and why you will not be there before the group meeting time. Also, you should volunteer to do more work.
Email provides a wonderful tool for coordinating schedules and conveying scheduling problems.
Both perceptions leave negative feelings. In many respects this is the flip side of the previous point. Social interaction during meetings is important. This helps group members become comfortable with each other, as well as enhances an understanding of where each group member is coming from. Of course, it is also important the group meeting does not become a social event only.