Document, document, document. As soon as you possibly can, write down everything you remember about the accident. Write down where you were, what time it was, what you were doing, who was there, weather conditions, etc. Also write down everything you remember being said at the scene by every person involved in the crash as well as the witnesses.
Also important to document are notes regarding your injuries, including any pain you may be experiencing, inability to perform routine tasks, stress or anxieties, sleep loss, etc. Do this on a daily basis following the crash.
The more detailed information, the better when dealing with the insurance claims process.