The first decision to make is what size the group should be. If your group is too big, it will be very hard to get it functioning as a group with a shared purpose, and facilitation will be more challenging. If it is too small, you may find that it becomes too close and you lose the diversity of experience that different people bring.
If you decide to have a smaller group, think about how you can be sure of capturing diversity. For example, you could have people on the group who also represent other groups or you may decide to do outreach to specific groups who are underrepresented.
Shona Brewster (NHS Lincolnshire Diabetes Project Manager) explains why just having individual representatives is not sufficient on its own: