First know the situation, is the person unresponsive try and alert the person and see if you can quickly tell basic signs. Are they breathing, are they unconsious. Time is of the most importance. CALL 911 ask for help fast and see if they can guide you to doing CPR, most can help you thru it. Remember the faster the response greater chance to help the person.
To start CPR
Tilt the head back and listen for breathing. If not breathing normally, pinch nose and cover the mouth with yours and blow until you see the chest rise. Give 2 breaths. Each breath should take 1 second
If the victim is still not breathing normally, coughing or moving, begin chest compressions. Push down on the chest 11/2 to 2 inches 30 times right between the nipples. Pump at the rate of 100/minute, faster than once per second.
CONTINUE WITH 2 BREATHS AND 30 PUMPS UNTIL HELP ARRIVES
NOTE: This ratio is the same for one-person & two-person CPR. In two-person CPR the person pumping the chest stops while the other gives mouth-to-mouth breathing.