1. Check the temperature.
Having a lot of people packed into a few rooms will make your house a lot hotter. Depending on the size of your space, even if the weather is quite cool outside, you may need to turn on your air conditioner. At the very least, turn the heat down — it's much easier to make the house warmer later if people are uncomfortable than to try to cool it down.
2. Turn on the music.
Every party, no matter how wild it gets later on, usually starts out with a few early guests standing around, making polite chit-chat. Having music not only helps set the tone for the party, it also helps fill in some of those awkward silences as things are getting started. At the beginning of the party, keep the volume low enough so that guests can hear each other — later, if there's a big crowd or you're in the mood for dancing, you can turn the music up.
3. Turn down the lights.
Your guests will have a hard time getting comfy at your party if your lighting scheme says 'doctor's office', so turn the lights down a little. Dimmers are great for this, but if you don't have those, turn on lamps instead of florescents. Light candles. Everybody looks good in warm, low lighting.
4. Put beverages and food where people can easily find them.
It doesn't matter that you have a smashing assortment of delicious craft beers if they're hidden on the bottom shelf of your fridge. Most guests, unless they're very comfortable in your home, won't go looking around for food or drinks — they'll gravitate towards whatever is easy to come by. So put food and drinks in a spot where they'll be easily visible and accessible to anyone just walking in. Try to put the food/drink table in a place where it won't be blocked by an accumulation of people later on — nothing's more frustrating than staring at a bottle of wine, just out of reach on a table that's three deep in chatty, immovable party guests.
If your drinks require ice, don't expect that your guests will somehow know to get ice from the freezer — get a small ice chest, or ice bucket, with a scoop, and place it on the table right next to the drinks.
5. Have a drink.
Or if you don't drink, grab a coke, or a few bites, or whatever it is that relaxes you and puts you in the party mood. You're the host, so your guests will be taking their cues from you. If you're stressed out, running around and trying to get things done, your guests will be stressed too. If you're relaxed, having a drink and enjoying yourself, your guests will follow suit. So have a drink, relax, and enjoy your guests and your party. You've earned it.
(Image: Jen SiskaErin & Danny Living Together in Only 500 Square Feet)