Commitment to a pre-arranged time and series of weeks in the beginning is essential. If circumstances cause a missed meeting, every effort needs to be made to contribute prepared material even though a member is absent. An unchecked, dominant personality can also kill group enthusiasm. The benefit of the group is found in mutual sharing. If one person dominates so as to hinder this exchange, maximum benefit will be missed.
Slim contributions can also be a difficulty.
If one doesn't do his homework and never brings more than a half page of handwritten notes to the meetings, it will drag the group down. A study group can get along in spite of such a deficiency but this person probably won't be asked to join next time. Each member should do his part. Dragging meetings out can also put a damper on effectiveness. Start on time, stay with planned time allocations, and end on time.