Some general points are:
Make sure you have got third-party liability insurance, which insures you against a possible claim against you if someone makes a claim. It does not insure the participants.
The route – and marshalling
Make sure you have enough marshals that you can rely on. It is good to have a very reliable ‘back stop’ marker.
Be very clear about the route, start and finish points and what time everything happens.
Stop every so often to allow the participants to regroup.
Plan for rain and strong winds.
Enjoying the ride
Don’t be too disappointed if not many show up.