Whenever I plan a party I try to do as much of the prep work in advance as possible so I can spend time with my guests rather that running back and forth constantly to the kitchen. To encourage mingling, set up stations where guests can help themselves to food and drinks.  If food is being tray passed, be sure the food is guest friendly; which means bite size and doesn’t require utensils.  Choose cocktails that can be premixed ahead of time and kept in pitchers waiting to be poured.  And most importantly, before your guests arrive, be sure the lights are dimmed, the music is playing, and the candles lit.  Relax, pour yourself a drink and enjoy!