If you are injured, call 911 right away. They will send the police and medical help if necessary.
Roadways can be dangerous places. Get out of your car and move to safety.
California Law requires you exchange information with other drivers. This means you should give your contact information and insurance information to other involved drivers. Make sure to get the other driver's information as well.
Document the scene with photos
In this day and age, many people have cell phone cameras. There is no such thing as too many photos.
File claim with insurance company
File claim with insurance company...BUT DO NOT GIVE A RECORDED STATEMENT. Insurance companies have one interest...settling your claim for as little money as possible. Insurance companies have plenty of resources and tricks to slowly chip away at the value of your claim.
Many lawyers give free consultations so take advantage of it.