1. First of all, try to not panic. In that type of a situation, cooler heads prevail, and the more you're able to deal with the situation, I think the better off you'll be. 

2. Secondly, ensure the safety of yourself and others. In California, if you're driving down the freeway, there are signs there that say if you're involved in a minor fender-bender, please move to the side of the freeway. And that's good advice. It it's situation where your vehicle is drivable, if you can move it, I would move it out of harm's way. In other words, if you're staying in the middle of the freeway, you're out of a vehicle, cars are going by, there's a high likelihood, a distinct chance that something else might happen, an another vehicle may hit you. So by ensuring the safety of yourself and others, if you can, move the vehicle out of any harm's way. 

3. Photographs are a good idea, if you get a chance before moving your vehicle, take photographs. All of us have phones now that you can pull out and take photos of pretty much anything, high quality photos. Take a photo of the damage to the vehicle, take a photo of the positions of the vehicle, take photo of the damage to your vehicle, all of these will help in the event there's a dispute to what actually happened.

4. Calling the police is a good idea, CHP a lot of times in the event there is no major injury they won't come out, they won't take a report. So you want to exchange all information with the other party. Most significantly, if there is somebody that saw the accident, comes up to you and says 'it's a horrible thing, it's not your fault', get that person's information. It's crucial. A lot of the times people walk into my office and they take it for granted that the police are going to find that witness, they're going to get the witnesses information and take a statement, a lot of time that doesn't happen. If you have a witness, get their name, get their phone number, get that address, you want to follow up with them in the even there's some dispute as how it actually happened. Other than that, you've done all you can at the scene, if you're injured, go get yourself proper medical care, and if necessary contact personal injury attorney in Sacramento like myself at the Law Office of Fred Sette a Auto Accident Attorney in Sacramento.  I can be reached at 916-710-8555 or fill out the contact form on our website.