The best thing to do is in January go do the Early Birds series. They will teach you the skills you need to race plus you will get to do some practice races. You can join a team at any time but its best to join a team before December. The reason for this is because most clubs get their clothing orders in around December. And then they don't get their clothes until like February or March. Pick a club that is close to where you live and there are many in this area. This way you can join the group rides without having to drive very far or at all. Some clubs have days were anyone who is a non-member can join the club for a group ride or others welcome non-members anytime. This way you can "try out" the club to see if you like them or not. This web site lists all the clubs in California:
http://www.usacycling.org/clubs/index.php?state=CA
You can narrow your search down based on city.