One tip: when you drive an automatic, you need to PUT IT IN PARK when you stop your drive! It's not like a manual--you can't just leave it in whatever gear you're in, put on the handbrake and leave the car. I learned to drive on an automatic but then swapped to stick and have been driving stick for the last 16 years. When you rent a car, though, you get automatics. Things to remember:
*You don't have to shift when you come to a stop sign/light. If it makes you feel more comfortable rest your hand on the shift, of course, but don't actually MOVE the shift.
*There's no clutch. That pedal you can hit with your left foot? Brake. Bad idea!
*The aforementioned "put it in park". Automatics won't let you remove the key from the ignition if it's not in park, also. If you can't get the key out, check what gear you're in.
*At stop signs/lights, automatics will creep a little bit forward if you take your foot off the brake. It's the kind of creeping you get if you're riding your clutch. Be sure you hold the brake when you're stopped.
*Right turn on red is legal in some places unless signed (ask). LEFT turn on red is not.
*Lane discipline: Californians have basically no idea what that is. Trust me, I'm a Californian! If you're going slower, stay to the outside (far right). Bunny-hopping from car to car will get you a ticket (excessive lane changes). Pick a lane and stay in it, adjust your speed to the car in front of you. Ideally, a car that is not speeding! Try to stay at the speed limit. Keep in mind that driving a rental car in some areas is considered a "ticket me!" flag, and your having a non-CA license makes it pretty much guaranteed.
*Another thing about CA roads-->roadsigns: If the sign overhead says EXIT ONLY and a yellow arrow points at your lane, the lane exits. Period. If there are two arrows, one white and one yellow, with an EXIT ONLY placard, the lane that is yellow (the far right lane) exits. The lane that is white splits and you can stay on or go off. If you want to stay on, be in a white-arrow lane.
*Do yourself a favor, merge at speed.