1. PULL OVER TO THE SIDE OF THE ROAD
There is very little reason to leave your car in the middle of the road after an accident. First, it is not safe. Second, it just creates another hazard for the other drivers. If your car is driveable, move it to the side of the road.
2. MAKE SURE NO ONE IS HURT
Before you can do anything else, you must see if anyone is hurt. If someone is hurt, do not move them. Call 911 and request an ambulance. Let the professionals provide assistance and evaluate the injured people.
3. CALL THE POLICE
I know they do not always come, but you should call them. Make sure that you tell them where the accident happened, and be specific.
4. TAKE PICTURES
Take pictures of everything. Take pictures of the accident scene, any debris, skid marks, your car, the other person's car and any visible injuries. You should always carry a disposable camera in your car for just this very reason!
5. BE PLEASANT!
It doesn't matter if the other person hit you when you are stopped. He feels bad about it already. Do not yell at him. Do not embarrass him. Do not humiliate him. Be nice, for one day it may be you who causes an accident.