Stop, Drop and Roll
Everyone should know this rule: if your clothes catch fire, don't run! Stop where you are, drop to the ground, cover your face with your hands to protect your face and lungs, and roll over and over to smother the flames. Do not run, this will only fan the fire.
If someone else's clothes are on fire, push them to the ground and roll them over and over; or smother the flames with a blanket, a rug or a coat if available.