When you call 911 an operator will answer stating "911 Police Fire or Medical Emergency" asking which emergency service you need. Depending on the service you need and the jurisdiction you are in, you may be asked to hold while the dispatcher transfers your call to the appropriate emergency service covering your area. When you call 911 be prepared to:
Tell the 911 operator what you need; ambulance, fire department or police department.
Be as calm as you can. When a caller is upset, it is hard to understand what he or she is saying or to get vital information quickly.
Stay on the phone.Do not hang up until directed to hang up.
Give your name and address and when traveling or away from home on a cell phone always be aware of where you are "next to the brown house across from the yellow one" won't help.
If your address is different from the location of the emergency, be sure to let the operator know.
In case of a police emergency, if possible, give the operator the suspects description, weapons, vehicles (license number) direction of travel away from the scene and anything else that may help description and license.
( Police FAQ's - Blytheville )