When you experience a car accident, it often disorients you for quite some time. In some cases, you may miss important opportunities because you simply don't know what to focus on in the immediate aftermath of the accident.
First, it is always important to address injuries sustained in the accident immediately. Even if you don't believe an injury is too serious, leaving it untreated may allow it to worsen over time. Similarly, you may suffer injuries that do not cause pain right away.
If you can do so safely, be sure to get as much documentation as you can of the accident scene. You can usually do this easily with a smartphone. If you do not have a smartphone, you may take pictures with any available camera, or look for security camera footage from nearby businesses.
Be mindful of what you say to any other party at the scene. Even a polite apology for the accident may get interpreted by the other party as an admission of liability. This is very dangerous. Even if you believe that you are actually responsible, it is important to remain calm and simply gather as much information as you can while saying as little as possible. The other driver may also believe that he or she caused the accident. If the driver admits as much, see if you can get it in writing or ask if it's ok to record the testimony.
Don't hesitate to reach out to an experienced local attorney. You may even find it useful to call the attorney to come to the scene of the accident and begin building your claim and protecting your rights immediately.