Throw a Cocktail Party
Lively and short—it may not be what you're looking for in a mate, but it's a good guideline for a cocktail party.
For "lively," you need to invite plenty of people, since a cocktail party should have a nicely buzzing kind of energy. There's no magic number of guests; it depends on the personalities and the space. Fifteen may feel crowded and boisterous; 40 may feel sparse. You just don't want it to feel empty.
"Short" means set a beginning and an end time—4 to 6, say. This makes it easier for guests to commit, and for you to say goodbye graciously when the mood starts to wane.