Do Not Leave the Scene. If there is vehicle damage, property damage, or damage to anybody... do not leave the scene. At times, you can even be charged by law enforcement for leaving the scene.
Get Medical Attention for Injured. If you see any injuries, no matter how small, call 911. Do not attempt to move an injured person unless absolutely necessary. If you move an injured person you can hurt them even more. Call 911 so a trained medical professional can handle the situation.
Document Everything. If you were in an accident with another vehicle, take all of their information; license plates, drivers license info, insurance info, make, model, color of car, copy of a police report, name, address, phone numbers, etc.
Give Statements to Only Police. Don't share stories with others, others involved in the accident, bystanders, etc.
Go to the Doctor. As soon as you are able, go to the doctor. You might think you feel fine, but it's best to get a professionals opinion. Be sure to document all visits and costs.
Call Your Insurance Company Dealing with insurance can be a hassle. The sooner they are aware of the situation, the faster they can help.