Never touch anything in a public area, and you'll be ok.
This includes stair handrails, escalator handrails, rental car steering wheels, elevator buttons, anything in a bathroom, free sample items at a store, shopping carts, anybody elses keyboard, floor models (of any type) at Home Depot, the coffee machine at work, forklift handles, previously dispensed straws at a restaurant, the community toothpick holder (right next to the straw dispenser), etc...
Oh, and never ever ever! use your tongue to flush the toilet at a bus station.