STOP! Anyone who gets into a accident must stop. Leaving the scene is considered "hit & run" and can be a felony. This includes hitting property, animals or pedestrians.
If the accident is a fender bender, emergency medical care might not be necessary. However, when in doubt, call (or ask someone) to call 911. If your first phone call was to emergency care providers, your second call should be to the police. The police will advise you whether it's required to move the crashed vehicles from moving traffic, and the investigating officer will take statements from the drivers, passengers and witnesses.
Write down the details of the accident and draw a sketch of the accident scene. Include the time of the accident, a diagram of the streets, what lane you and the other vehicles were in, the direction the vehicles were traveling, traffic signs, and obstacles in the road. Draw a picture of your vehicle indicating damaged areas.
Even if the facts of the accident are embarrassing or detrimental to you, tell the truth. If you alter your story down the road or you don't disclose pertinent facts, the insurance companies involved will find out. That could come back to haunt you! The insurer can deny coverage or shift more fault to you.
You also should get the investigating officer's contact information for future reference. The officer's report is not available at the accident scene.