Take Pictures- As Soon as you can Safely do so, For Later Determination and Proof of Cause of Accident
If you can take pictures of the cars involved, immediately after the accident, do so. This will prove invaluable later to either confirm or dispute the findings in the police report. Take as many pictures as possible from as many angles as possible, with references in the frame, such as curbs or streetlights and signs.
If you are in traffic, it may not be reasonably safe to do this for very long. Always put your safety first.
Call for Help- Use Your Phone as a Phone and Call for an Ambulance and Police
If you or someone else is injured, call for an ambulance. Do this before taking pictures, you will have time while you wait. Use the maps or GPS on your phone to give the dispatchers your exact location.
Document name, address, telephone number, driver license number of all drivers involved
Use your note taking application or better yet--Use your camera again! Take a picture of the other parties drivers license, business card and insurance card. Note the make model and color of all vehicles involved. Better yet--photograph the make and model. If you are shaken up, and cannot write things down video or record a note. You can always combine them later with Evernote, or similar application.
Videotape Witness Information and Statements
You can jot this information down in your note taking application. Better yet, videotape it-- get the witnesses: names, numbers, and addresses where they were when the accident happened and what they saw.
Use it as a Phone Again--Talk to an Attorney
After you and others involved have gotten medical attention, talk to a lawyer. Find out where you stand before you talk to insurance company adjusters or give any statements.