Nope, just show up. It's informal, most of the riders have been doing it for years. What usually happens is the older guys roll out 5-10 minutes before the main group goes, rides a little bit slower and gets absorbed somewhere before La Tuna. If you're in the parking lot at 8 ready to ride, you can roll out with either group. The group sort of regroups at the top of La Tuna and there are a couple of sprints that happen through Glendale. I'd recommend staying out of the middle of them until you have a better sense of the group.
And you should check out the H&S shop rides. The rides are no-drop. That's the shop I hang out in and the club rides are fun. I think they are only once a month.