The BBC has a series on the future of medicine wherein it looks at some of our current practices and evaluates their efficacy. Here are its views on some common situations: 

MYTH 1: Put butter on a burn
MYTH 2: Giving chest compressions to someone who doesn’t need them can cause more harm than good
MYTH 3: To do CPR properly, you need to give mouth-to-mouth as well as doing chest compressions
MYTH 4: You shouldn’t shock someone with a defibrillator unless you are certain their heart has stopped
MYTH 5: Tilt the head backwards to stop a nosebleed