It might have already have been said but if you do get stopped by the police/highway patrol/sheriff/any LEO, then do not suddenly rummage around in the glove box or make to get out of the car as they are walking towards you as some LEOs get a little nervous about it. In my very early days of driving in the USA I did this and the sheriff's deputy started to reach for his gun. Told my American co-workers about it and they said just sit in the car with your hands on the steering wheel until he comes up to you which is something I have done since - but certainly no rummaging around in the glove box etc. This is a good guide: http://www.dmv.org/articles/traffic-stop-dos-and-donts/
And never refer to CHP as "CHIPs" in any conversation unless you want to sound like a stupid tourist!
You might find this moderately useful/amusing: http://www.californiadriving.com/
But what I will say about driving in the USA is that there is usually so much room, and much clearer signage, that if you do mess up it is not as bad as in the UK, and that the general standard/approach to driving is so much worse than the UK that even if you were driving on the wrong side of the road then you still wouldn't be the worst driver out there !
Oh, and one last thing, don't get angry with other drivers just in case they have a gun ! (wife, you listening????!!!!!).