Speaking from my experience as a member of a rescue that runs around seven hundred calls a year there are several things that the people or person calling for help can do to assist in the situation.
If the 911 operator cannot understand what you are saying because you are hysteric then there is nothing they can do to help you. Sure they can call the police department and say they have a call from at distressed person at the address where the phone call was made. That's fine if you needed the police but what if your house was on fire?
If you need an ambulance because you think you or someone else might be having a heart attack then EMS personnel are going to have to find you. If your house sits away from the road, or maybe is painted a different color then the houses tell the 911 operator that so it is easier to find you. For example “I need help I think I am having a heart attack I am at 123 ABC street, the house sits back behind the tree line with a long dirt driveway leading to it,”.
A detailed description like that allows the ambulance crew to better confirm they are going to the correct house, especially if the houses are not numbered, or numbered badly. If possible have a bystander meet the ambulance outside this is especially helpful if you live in an apartment building so it is easier to find the sick or injured person. It will help with treatment time so that the ambulance crew does not have to count apartment numbers and go up and down each floor to find the right one
Early recognition of a problem is essential in receiving sometimes life saving early EMS intervention such as beginning CPR or the use of a defibrillator. It takes time to respond to a scene and keep in mind that when seconds matter the quicker help can arrive the better.
First someone has to recognize the need for medical assistance, and for arguments sake lets say that takes 2 minutes. Then you must call 911 and explain to the operator the situation you are in which will take another 1-2 minutes. After that happens the 911 operator will contact your local EMS dispatcher and explain what you just told them, this will take another minute. Finally the EMS dispatcher will send out a tone for the rescue squad or ambulance service which they will explain what the call is and where it is located, and lets say that takes 30 seconds to a minute. If you are lucky and your ambulance service is fully staffed and requires its members to stay at the building on shift then they will be en route in three to four minutes. If you live fifteen minutes away the ambulance might be there in ten to twelve minutes with the lights and sirens going.
If all of this happens without complications then the ambulance will arrive to help you in around seventeen to twenty minutes. This is a long time to be having a heart attack or not breathing so the quicker you can ask for help the quicker help will arrive.
