Play fun music. Remember this isn't a club, but you don't want soft jazz if you expect your guests to stay awake. Unless it's a soft jazz party.
Remember your crowd, who are you playing for? Is it a Christmas Party? If so, play Christmas music! Is it a dinner party, play something soft, maybe light rock... but don't play club-hard-rock-heavy-metal to a dinner party for your closest business associates.
Have the ipod already set and playing 30 minutes before the party is set to begin... this way you aren't "radio silent" when your guests arrive early.