What to find out in advance: Which top bananas will be there, so you can think up something smart to say.
What to give:

Remember the classroom rule: If you don’t have gifts for everyone, don’t hand them out in front of everyone. If you’re giving presents to only some of your coworkers, do so at another time.

What to do:

Introduce yourself to the company bigwigs, suggests Anne Fisher, who writes Fortune’s Workplace column. If they seem busy, just add that you enjoy working there, and move on.

Listen more than you speak. Avoid conversations about politics or religion with coworkers you don’t know well.

Consider sticking to club soda. “Nobody’s the talk of the office for eating too many cheese puffs, but anyone who gets looped is discussed forever,” says Margo Howard, author of Slate’s Dear Prudence online etiquette column.

How to dress: Upgrade your normal office look. Accessorize a suit with an evening handbag and pumps, suggests Jennifer G. Wolf, a fashion consultant in Ann Arbor, Michigan. If you normally wear pants, a black skirt and a twinset should do the trick.
Coming and going: Don’t be fashionably late, Fisher says; arrive no more than 10 minutes after the start time. “You don’t have to wait for the boss to leave before you do,” she adds. “No one’s watching the door.”
How to follow up: If someone took trouble to plan the party, a thank-you note would be thoughtful.