There's a lot of snorkeling spots within the shores in Southern California. For tourists snorkeling the very first time here, La Jolla, north of San Diego, is certainly ranked as one of the top 10 destinations on earth for snorkeling.
Dive Knife. They can be a Life Saver if you or your friends get caught on kelp. Always Have One when you go diving. Watch your friends while they dive, take turns diving, and be sure they come back up safety.