If you've been in a wreck, the situation is pretty chaotic. However, to the extent you can, here are a couple things you want to do right away:
a) if the police are present, cooperate with them and give them a statement that is specific as to how the accident occurred and what the other driver or drivers did to cause the accident;
b) if witnesses are present, get their names, addresses, phone numbers, email addresses, etc., and, ideally, ask them if you can record a brief statement on your phone as to what they saw as to how the crash happened, what each person or car was doing, how bad the impact was, and what any of the people involved in the crash had to say right after the accident. While you are at it, take photos of every vehicle involved in the crash to show the damage that was done. Also take photos of the scene and particularly any road debris or tire marks, road signs, etc.; and,
c) if you talk to the other driver, be polite, but be sure to exchange information so you can get that person's identity and contact information, ideally the registration number for the car, its make and model, and the license plate number. Write down anything the driver says about how he or she thinks the crash occurred. Make sure you find out which company or companies insure the other person's car. If that person has an insurance agent, write that information down, too.
If you are not injured seriously, thank your lucky stars and try to work through the claim with the opposing party's insurance agent and adjuster. If you are injured enough that you will need to miss work, have surgery, or have significant medical bills, look to see an experience trial attorney who handles these types of cases. Do NOT delay --- time is not on your side. Also, many times car crash victims will begin to experience aches and pains, bruising, and other indicators of injury 12 to 36 hours after an accident. As soon as you experience any such symptoms, head in immediately to either the local emergency room or your family physician.