Prep the bathroom with candles, fresh towels and plenty of toilet paper.
Determine the flow and place food accordingly; people generally congregate in the kitchen if not told otherwise. But, kitchens are the staging area so tend to collect the mess. Guide people with food and music.
Music is important. Take the time to curate a playlist and have it softly playing in the background.
Lighting should be soft, not intrusive or too casual — lamps and candles usually do the trick. Skip overhead lighting unless you can dim it.
Designate a few "helpers." Friends that can help fill drink, that notice when a bowl of nuts needs refilling, that can take trash from guests.
Rearrange furniture to get intimate conversation areas going and open up pathways for guests if needed.
Have trash discreetly available in every room.
Plan for a place for coats, umbrellas and purses.
Have extra plates and napkins always available (napkins always go faster than you think!).