At the scene
Call 911. Even if no one is obviously hurt, a police report creates an official record that will matter later. Do not say "I'm fine" or "I'm sorry" — both are routinely used by insurers as admissions.
Photograph everything: vehicles from multiple angles, debris field, license plates, the other driver's insurance card, road conditions, weather, traffic signals, and any visible injuries. Get the names and contact info of every witness.
Within hours
See a doctor — emergency room, urgent care, or your primary doctor — even if you feel okay. Adrenaline masks symptoms for 24 to 48 hours, and a same-day medical record is the single most valuable piece of evidence in your case.
Notify your own insurance company that the accident happened. This is required by your policy. Do not give a recorded statement to the other party's insurer. Politely take their information and tell them an attorney will be in touch.
Within the first day
Start a written record of everything you remember about the accident and how you feel. Save every receipt for medical care, prescriptions, transportation to appointments, and damaged personal property. If you miss work, document each missed shift and your normal pay rate.
Common mistakes to avoid
Do not post about the accident on social media — anything you say will be used against you. Do not accept a quick settlement offer from the other side's insurer. Do not skip follow-up medical appointments. And do not wait more than a few days to consult a personal-injury attorney.