Soap and friction
Wet your hands, use soap to lather and rinse away with warm water. While scrubbing your hands, be sure to clean under/around the nails, between your fingers and up onto your wrists.
Some people like to scrub while they say the alphabet or sing 'happy birthday' a couple times to ensure they are washing
long enough. Air and towel drying (if clean) have no difference in contamination rates.