When entertaining we ask that guests do not smoke inside our home, and politely step outside if the desire arises. We also ask that everyone take off their shoes upon entering and leave them in the stairway entry. And finally, we just ask visitors to not leave any of the doors open, since our cats are strictly indoors, and we wouldn't want them sneaking out or another feline sneaking in (which has happened). Other than that, visitors are free to breakdance, rearrange my toy collection (okay, maybe just infants and children), and relax/snoop to their heart's content.
We've been in some households where there are a variety of house rules in effect: keeping voices at a minimum at all times, having to always carry and use coasters, guests asked not to bring children, no drinks while sitting on furniture or ontop of specific rugs/flooring. All valid worries manifested into enforced rules of the house, though it can be a damper for some (especially those who liked to get a bit tipsy-nipsy Russell in the house). How about you? Do you have specific "house rules" that you make sure to enforce with guests? Any memorable situations where rules were broken?