Check the scene for any potential dangers.
If the scene is safe proceed to check for responsiveness. To do this, tap the person on the shoulder asking if they are ok/if they need any help. If the person needs help continue with these steps.
Either you or another bystander should call 911, remain on the line the entire time as they will assist you.
Check for breathing for no more than 10 seconds, if the person is not breathing, occasional gasping for breath, has no pulse, or is unconscious you may begin CPR
Place one hand over the other and interlock your fingers. Directly place the heel of your palm on the person's chest/lower breast bone
Begin a set of 30 chest compressions. If the victim is an adult or child these compressions should be at least 2 inches deep (for a baby only 1.5 inches) and at the rate of 100-120bpm.
Lie the person on their back and tilt back their head to lift the chin, this open's airways.
Pinch the victims nose and lift the chin and deliver two breaths. Make sure there is a rise in the chest after the first breath, if not you may need to reposition.
Continue cycling through steps 8 and 9 until medics arrive or until the victim regains consciousness