There are many sites and also instructables showing what to do after a car crash. I will show you the newest and easiest way of handling the situation you are in after a car crash.
66% of all people recognize a cardiac arrest or an apnea but only 22% know what to do. In fact the things you learn are too theoretical, too overstraining.
Also, in 1997 the European Resuscitation Council that it is of no matter how you do the recovery position.
So, I will show you in some steps you should be able to learn because of their inner logic how you can really help instead of being paralyzed by thinking of how something just be done or just your fear to hurt the injured people even more.

Disclaimer: I am not responsible for any damage you will effect by following the next steps. But to make it short: For example in Germany there are about 1200 accident victims needing help and there is no reported case in which a first aider got arrested because of doing something wrong.

You don't have to do all right (you are no doctor) but you should do something at all. In most cases the forces that have been unleashed while the accidents were much bigger than the forces you can do to the victim.

The pictures are all from Wikimedia Commons the authors are mentioned in the particular steps. Thanks to all.

Pics ©: Thue
and Alexander Augst

Step 1: Safety First. Ensure Yourself, Than the Victim and the Scene of the Accident.

Ensure yourself, than the victim and the scene of the accident. Otherwise there is the risk of following accidents.
Park your car with adequate distance, switch on your warning lights and position the warning triangle.

Then get a general idea of the situation. How many people are injured or involved into the car accident? Are people jammed in the car?
Call 911 or in Europe you can call 112 from a mobile.

Connected to the rescue service you got to calm down, listen to the operator. He will ask you the questions (computer aided) he will need answered by you. Don't hang up by yourself, the operator always will end the call. Always wait and follow the operators instructions.

Pics ©: Bastique and
Mattes, Ernstl and the last one is public domain.

Step 2: Keep the Crash Victim From Cooling

There is a coherence between body temperature and the chance to survive after the car crash.
So, don't take the crash victims clothes off. Instead warm it with a jacket or a blanket, maybe the first aid blanket with the golden and the silver side.

Pics ©: Markus Brunner

Step 3: Be There for Them.

Holding hands and calmative talking are very important. Indeed you should take care of the victim first physically. But when there are enough people to help, than somebody should take care of the victims psychological condition.

Pics ©: Elizabeth Ann Colette

Step 4: The Recovery Position.

The recovery position is often overrated in firts aid courses. A reanimation is sometimes more important than the recovery position. There are many sites that show the recovery position. If you can't remember how to establish the recovery position in the situation of a car crash, just do it. The way you establish the recovery position is not important. Of importance are 2 things:

1. the mouth has to be the deepest point of the body.
2. the neck has to be overstretched.

If your "patient" is in the improvisational recovery position you still have to check if the victim is breathing.

Pic ©: Rama

Step 5: Take Off the Helmet.

There are many instructions saying that you must not remove the helmet of an bike crash victim. But if the biker is without consciousness and you can't check if he is breathing, take off the helmet. Be careful, hold/support the neck and remove it. If you are alone - get help. In Germany there is the rule HONDA (Helm abnehmen ohne nähere Diagnose, which means Take off the helmet without particular diagnosis.) Again just support the cervical spine. The head must not turn to one side or another.

Pics ©: Author and
Serenity

Step 6: Just Do It.

Yes, Nike is right.
Doing is better than not doing. You can't be more dead than dead, so there is only one mistake after a car crash - to do nothing.

Pics ©: Johannes Pietilä

Step 7: Don't Interrupt the Cardiac Massage.

If you are in charge to make a cardiac massage, it is important to do a continuous cardiac massage without any large interruptions. Studies have shown that the cardiac massage lose quality after 2 minutes. So, if you are not alone, change the massager without interruption.

The cardiac massage is more important than a right rescue breathing. In the first 3 minutes there is enough air in the lungs you can circulate through the body by an adequate cardiac massage.
Don't interrupt the cardiac massage for taking the pulse. Just do the cardiac massage until the EMS is there.

The frequency should be about 100 presses per minute. The position of the hands is irrelevant. Just hit the middle of the breastbone.

Pics ©: Kalumet, Bionerd, first torso: Morne, second torso: Clawed

Step 8: Don't Ligate Wounds.

Don't do ligation on massive wounds. After ligation the blood agglutinates what complicates the reopening of the wound or the vasodilations.
Also sinews and nerve fibers could be damaged.

Hold the wound up. Use a compressive bandage. Just take bandages an press them completely onto the wound with pressure.

Pics ©: Brian Snelson

Step 9: Don't Take the Pulse.

It is a waste of time. You have to do something even though you think the patient has no pulse. So the pulse frequency will show you nearly nothing. Just follow step 7, if the patient breathes abnormal or if he don't breath.

Pic is public domain.