Seems the most logical forum, since your questions are about beauty and fashion.
As ST said, a "little black dress" would be perfect but you can also stand out in something jewel toned since the "LBD" is sort of ubiquitous. You don't need something full length (I think very few women wear long gowns all that much any more) so you can do knee length or cocktail length. As for the rest, you should still look like yourself - basically a hairdo similar to what you wear most of the time, maybe poufed up a bit or made a bit more special but you do want to be comfortable and also still look like yourself. As for makeup - go with your "every day" type look but a little amped up - a red lip, a bit "more" colour, shadow, etc. ST mentioned the "smokey eye" and that could be an okay look except that for a lot of us, we end up looking either like we've got 2 black eyes or we've just emerged from the crypt, so if you don't normally for for that sort of look or if you're say, 35 or over, be very, very careful.