Starting up OA in our Troop

Our Troop has traditional not participated much in OA. I can think of only one Scout who was a member, and we currently have none. We are trying to get it started again, but we (the current leadership) know little or nothing about it. A couple of questions to help get us started:
1) Who selects boys for membership and when?
2) What are the "real" criteria for selection? Should every boy who is eligible (has satisfied the camping requirement) be selected? I guess I could see it both ways. I keep explaining to the boys that Scouts is about the only organization they will ever particpate in where the requirements for promotion/advancement are spelled out in a book, and they get the promotion when they complete the work. No "this guy has a bad attitude, let's not promote him" except in exceptional circumstances. On the other hand, we really have no way to reward Scouts who clearly go above and beyond. Maybe this is one way?
1) Who selects boys for membership and when?
2) What are the "real" criteria for selection? Should every boy who is eligible (has satisfied the camping requirement) be selected? I guess I could see it both ways. I keep explaining to the boys that Scouts is about the only organization they will ever particpate in where the requirements for promotion/advancement are spelled out in a book, and they get the promotion when they complete the work. No "this guy has a bad attitude, let's not promote him" except in exceptional circumstances. On the other hand, we really have no way to reward Scouts who clearly go above and beyond. Maybe this is one way?