The first step is to stay calm. It will probably be the hardest thing to do but by staying calm you will be in a better position to help others and remember key details that may be important later to your insurance agent or lawyer. Staying calm will also help you to physically document details.
Next, before you start any documentation of damages call 911. Then see if there is anyone injured that needs help immediately. Also, if you are in an area where it is dangerous to leave your vehicles you will need to try and move them if possible, otherwise leave everything as-is for the police officer. Once you are able to make sure there are no immediate emergencies to tend to, go to your glove box and grab the disposable camera, pen and pad of paper you keep in there for the specific purpose of documenting damages in a car accident or crash.
Pictures and Written Documentation
Go ahead and start taking pictures as soon as you can before anything gets moved by the police officer or the other driver. After you feel like you have taken plenty of pictures, quickly jot down your remembrance of the accident. If there are any witnesses, get their names and numbers along with an account of what they saw. You also need to get the names and numbers of everyone involved in the car accident and their account of what happened. Don't argue with them if you disagree... just try and stay neutral and tell them you just want to make sure everything is documented for insurance purposes.
Cooperate with Police
By this time the police officer should be there. Cooperate with the police officer fully and always request and accident report. Sometimes doing this much documentation may be uncomfortable for you and the others but it can be vital in processing insurance claims quickly and/or if you were to get sued due to the car accident.
Here are some additional things to consider when documenting the extent of a car accident's damage and injuries:
1. List missing or damaged personal items you kept in your car such as electronics, glasses and contents of your purse or wallet.
2. Make sure to document how you feel physically, however insignificant. Sometimes a small back ache from a car accident can lead to serious back problems just a few days later. Try to document this same medical information about all persons involved in the accident.
3. Taking pictures of everything is important and pay particular attention to looking for skid marks and other things that were damaged in the car accidents such as light poles or trees and document the damage with photographs.
4. Don't sign anything unless you are fully aware of what you are agreeing to. If you don't understand what you are asked to sign, by anyone, it is best to contact an accident lawyer to help you. Also, only discuss the details of the car accident with the attending police officer and do not admit guilt. The specific details are all that is needed and the insurance companies and/or lawyers will determine who is responsible for the damages.