The first few days immediately following an accident are often the most important for finding and preserving evidence of what happened -- and documenting your injuries. You should take the following steps as soon as you are able, to make sure your personal injury claim is as strong as possible.
If an accident occurred somewhere other than in your home, return to the scene as soon as possible to locate any evidence and photograph any conditions you believe may have caused or contributed to the accident. You may be amazed to find something you were not aware of when the accident occurred but which may help explain what happened, like a worn or torn spot on which you fell or a traffic light that isn't working. Also, while looking around you may find someone who saw what happened or knows of other accidents that happened in the same spot.
Take photographs of the accident scene from a number of different angles -- particularly your view of things right before the accident -- to keep a good picture of it in your mind and to give to the insurance company later on to indicate how well prepared you are to get the settlement you deserve. Photograph the scene at the same time of day as your accident occurred, and for vehicle accidents, the same day of the week, to show the appropriate amount of traffic.
Fault for an accident is sometimes established by a piece of "physical" evidence -- something you can see or touch, as opposed to a description of what happened. Examples include a broken stair that caused a fall, the dent in a car showing where it was hit, or an overhanging branch that blocked visibility on a bike path.
In addition, physical evidence can help prove the extent of an injury: Damage to the car can demonstrate how hard a collision was, for example, and torn or bloodied clothing can show your physical injuries dramatically. Try to preserve any physical evidence exactly as it was at the accident. If you can't preserve the actual object, take photographs of it. You can later show your evidence to an insurance company as proof of what happened.
A witness to an accident can be immensely valuable to you in making your case to an insurance company. Witnesses may be able to describe things about an accident that confirm what you believe happened, backing up your story. Also, they may provide you with information you were not aware of but which shows how the other person was at fault. Even a witness who did not actually see the accident may have seen you soon after you were injured and can confirm that you were in pain or discomfort. Alternately, a witness may have heard a statement made by another person involved in the accident indicating that someone other than you was at fault.
However, time is of the essence. If witnesses are not contacted and their information confirmed fairly soon after the accident, what they have to say may be lost. People's memories fade quickly, and soon their recollections may become so fuzzy that they are no longer useful. Also, a witness might no longer be around if you wait too long; people move frequently.
The best ways to preserve evidence of your injuries are by promptly reporting all of them to a doctor or other medical provider, and by photographing any visible marks, cuts, bruises, or swelling, including any casts, splints, bandages, or other devices.
Without an early medical record of all your injuries, and photos if possible, it will be more difficult to later convince an insurance company that you were injured in the ways and to the degree you claim you were. Visible injuries heal and will not look as serious later, and failing to seek immediate treatment can lead an insurance company to believe that your injuries were not so serious, or even that you invented or exaggerated them after the accident.
You can turn to How to Win Your Personal Injury Claim, by Joseph Matthews (Nolo), for a guide that will show you how to handle almost any accident situation and what to expect at each step of the insurance claim process.