I would hold the door open for other people coming in who probably don't want to wait behind me, then enter myself and stand in the doorway so I could observe the room. If I meet the eye of anyone I recognize, I would smile in a reserved yet amiable manner typical of me in large social settings. I would probably go out of my way to greet those people first, perhaps listen intently to the conversation (or pretend to) a bit before moving on to listen to other conversations and greet people who look interesting. At some point I would get bored and start to look for ways to get some value out of my night-- probably get some water or maybe a drink and either look for another loner who looks interesting to talk to, or look for a good discussion that I'd actually want to get involved in.
Though-out the evening I probably wouldn't talk much. I'd smile a lot and pretend to find the whole thing interesting, but after long enough if nothing fun was going on, I'd slip out quietly... perhaps go jump in the pool, explore a nearby forest, or shoot some hoops out on the driveway if I could find a basketball. If I'm lucky the hosts will have some kids who can show me something more interesting to do.