The transition from the typical OW diver to a GUE diver is a big one. Unless you were lucky enough to be started in, or buy GUE-compatible gear, you will be changing equipment. You will almost certainly be encountering new concepts, ranging from equipment balancing to minimum gas and dive planning. You will have to learn a much higher degree of situational awareness and sense of diving as a team, as well as the whole set of ideas about how that is successfully done. This transition can be significantly eased by diving with divers who have done it before you, who know where the bumps in the road are.
The entry-level GUE class for already certified divers, GUE Fundamentals, is a very hard class to pass if you come to it with no training but the typical open water/AOW/Rescue sequence. Most people want to pass the first time through, although it wouldn't be as critical in Southern California, as you have a number of local instructors. But to pass the first time through requires learning a lot and practicing it before you even take the class (something I actually rather deplore) and requires mentoring.
Most of us hooked up with GUE-trained divers, or as now happens in Seattle, connected with a GUE community that runs open dives. Bob Sherwood has given you the names of the folks to contact in your area -- they are all active divers and teachers.
