Didn't Richard Pryor do part of his stand up act on this???
"You think I am gonna put my mouth on his?..."
Make sure the airway is clear. If it isn't, then clear it.
See if the person is breathing. If the person isn't breathing, then supply air by whatever means are available (including mouth-to-mouth, but preferably a bag).
Check the pulse. If there is no pulse, begin chest compressions. This overlaps with the breathing.
They also taught us that that by the time CPR is necessary, there is only a 1 in 10 chance that the patient will survive. But that's better than nothing.
It's an easy class to take, but the application in real life can be be a bit messy.