Sorry to be a wet blanket, but there's a couple of things I'd like to add, based on advice from my solicitor when I was involved in a 'club'. Unless you have public liability insurance avoid having rules. Rather outline YOUR plans for the day, if others follow you then so be it. If you do choose to have rules then you need to ensure you also take all reasonable steps to ensure the route is safe and either hazard free or that all participants are made aware of any hazards. Make sure that it is clear that riders are to obey all road laws and ride according to the conditions and their skills. You will also need to make sure everyone on the ride holds the appropriate licence for the bike they are riding and that said bike is registered. As the 'organiser' you are ultimately responsible for the safety of those on the ride. Yes that's right, you have a duty of care.