Always identify yourself to emergency response personnel.
Do not hinder the duties of law enforcement, EMS or fire personnel, by blocking traffic from entering/ leaving the scene.
Remain
out of the way until the incident is under control. Refrain from tying up
emergency personnel with questions. After the incident is under control, personnel
may be willing to answer questions.
You may take photos as long as it doesn't interfere with emergency personnel.
Emergency
personnel at the scene are trying aid the injured, or conduct an investigation.
When asked to remain away from the scene, they are not necessarily hiding
things from you, but may be trying to preserve the integrity of the scene.
Show courtesy toward victims and suspects that do not want their
photograph taken.
If the area is a crime scene, or under investigation ask where you may go.
If you enter a restricted area, you may be arrested.
One way you might get in with local police and fire personnel is to stop by
their station when they are not on a call and introduce yourself. Let them
know who you are and that you are more or less on their side.