What do you do in a situation like this? The first thing to do as a first responder is to keep calm yourself. Quickly assess who needs assistance first. Do not move victims unless they are in a dangerous situation. If the victim is conscious ask simple questions: "What is your name?", "Are you in pain?" "Do you know the date?" While you are doing this, make sure someone else is calling 911 for assistance. If other people are around, instruct them to make sure traffic is diverted to avoid more problems.
If someone is bleeding, try to find a clean cloth and apply direct pressure to the area. Do not worry about hurting them if there is a wound. The victim will not feel the pressure as pain and it may just save their life as blood loss is one of the more serious outcomes of trauma. Try to be reassuring as much as possible with statements like, "You are going to be OK", "Help is on the way", "I will stay with you, don't worry".
If there are many victims try to deal with the most seriously injured first. Try to keep the victims on the ground (sitting or lying) and calm.
Today, I practiced all of these techniques. I stopped the facial bleeding (with her own scarf) and made sure there were no serious hidden injuries. I assessed a broken hand and that there was no obvious neck or head injury. She was crying but was able to answer simple questions. I kept the victim quiet and reassured as much as possible until the paramedics arrived to transport her to the hospital.
I will probably not know how this accident or the young woman who was hurt turned out. When the paramedics arrived, I just removed myself from the scene and went on with my busy day.