For a housewarming party in a small space I'm imagining some food, plenty to drink and lots of nice people.
Clean up. People will be snooping and there's never a second chance to make a first impression.
Use the Coffee Table as a table. Clear it off and keep it stocked with napkins and space for people's drinks. Or set it up like a buffet for people to circle around and eat off of like gregory used to do.
Alternative Seating like stools, poufs and pillows on the floor will open up space for people. You can also just make them stand!
Set Up The Bar with enough room around it that people can gather. There's always a crowd so don't put it right by the front door where people are going in and out.
Keep the Lighting Flattering: there is nothing less flattering than an overhead light. Get the lamps on, have them on dimmers or switch out the bulbs for a lower wattage. Don't forget to address the lighting in the bathroom. And while you're at it, you might want to depersonalize the bathroom a bit too.
Party Proof The House . Especially in a small space where people will be bumping into furniture, etc. move the breakables, or at least anchor them with some earthquake putty.
A Place for Coats and Bags. My living room is so small that if two people came in with coats and bags, then I would have to turn people away, I'd be full. So without a coat closet, that means it all goes on the bed. This frees up tons of space and means I can invite more people ;)
Shoes on or Off this is always a raging debate, but decide ahead of time and make sure you've got room for people's shoes and perhaps give them a courtesy heads up that their socks or feet will be on display for the party.
Music: Grace is our go-to for music advice (see here so she's the first to point out the importance of your party playlist. Don't leave it till the last minute. And put it on a half hour before guests arrive so that you get into the party spirit.
Stock up on Supplies like toilet paper, paper towels or dishtowels, and plenty of trashbags. And make sure the trash is in a convenient spot. How many times have you been at a party, been done with a napkin or a disposable plate or glass and had no idea where to throw it away?
Image: Beth Ziegler