Alot of the time there is a theme or an outfit is appropriated by an activity you will be doing. You are certainly going to dress differently if it is a bowling afternoon than if it were an evening cocktail do. Or God if you aren't definitely keep reading!
What you should be working towards is sophisticated glamour. Wearing a blazer over a dress creates this look immediately. You want to use a nice tailored jacket, not the one you wear to work every day. A plain black dress with a metallic boyfriend blazer takes things to another level.
Avoid showing too much skin at all times, anything too tight or anything you feel uncomfortable in and have to keep pulling down at the hem or up at the top. While you are there to have fun, and by all means let your hair down a little, you still want your boss and colleagues to look at you like a professional.
Wearing your hair up with some bling earrings or necklace (not so much if you opt for a metallic blazer) makes a high impact statement. While a bold lippy has authority.
(definitely go for a longer hemline than this, but you get the drift)