New York ? The excitement begins when you open the mailbox to find a fancy envelope with your address written in calligraphy. Then as you carefully open the flap, so elegantly held together with a seasonal seal, you can hardly keep yourself calm enough to gingerly remove the embossed invitation inside.

You are going to a fancy party! Hooray!

But daydreams of the well-heeled crowd drinking champagne from crystal glasses turn to dread when you read the fine print: “Festive attire.”

What does that mean? A hat with bells on it? Balloons attached to the spaghetti straps of a dress?

“‘Festive attire?’ No one really knows what that means,” says Peggy Post, an author of etiquette books and the great granddaughter-in-law of etiquette guru Emily Post. “It could be anything from nice work attire to a cocktail dress to holiday-themed jewels.”

Lesley Jane Seymour, the editor in chief of Marie Claire, says stylish women now have so many choices for party dresses that many end up throwing up their hands and claim they have nothing to wear.

“Having no more rules in fashion was liberating for five minutes, then everyone has to figure out their personal style, which is very hard to do,” Seymour says.

A strict black-tie dress code makes things easier for men ” a tux is a must ” but it is can still be ambiguous for women because ball gowns and cocktail dresses could both fall into that category. And both could also be inappropriate.

“Black-tie optional” is usually a more-than-subtle hint urging people to wear very dressy clothes but without insisting men buy or rent a tuxedo if they don’t already own one, Post adds.

To make sure you don’t a fashion faux pas, Post, the spokeswoman for the Emily Post Institute, a “civility barometer” for American society, encourages guests to ask their hosts for further guidance.

“I’m all for asking the host, ‘What are you wearing?”‘ says Post,

PICKING THE RIGHT PARTY CLOTHES DEPENDS A LOT ON THE PARTY. When you don't know many details, consider an outfit that spans different levels of formality, such as Anne Klein's fancy beaded skirt and more casual sweater.

She says even if you don’t know the host of the party well, it is always OK to ask about the dress code, but, she acknowledges, sometimes it is hard to know who to ask if it’s a charity or business function.

The next clue could come from the venue.

If a party is being held in a ballroom of a hotel, for example, it probably is a formal affair that calls for a fancy gown, according to Post, while a party in someone’s home is typically more casual and a shorter cocktail dress or even a suit would do.

Post has some rules, though, that apply no matter the outfit nor the event, including choosing clothes that are “age and leg appropriate.”

If the party is related to work, steer clear of anything too sexy or outrageous; stay professional but don’t wear typical office attire, either.

Seymour, who includes a “Big Bash” eveningwear section in the December issue of Marie Claire, guardedly approves of wearing a miniskirt or pants (only with heels, please) to even the fanciest black-tie parties “as long as it’s an overall glamorous look.”

To best match an outfit to the tone of the party, Seymour says to look at the whole package. “It’s more about how dressy the fabric is than the silhouette. Satin and beading are safe, also lame and sheer. If it’s a dressier event, go luxe ” beading or brocade. Working backward to less formal, you could wear satin pants with a beaded tank,” she says.

Mixing and matching moods also helps an outfit span a variety of occasions. For example, during a recent Anne Klein runway show models wore sweaters to temper very fancy ball skirts.

Still, a simple black strapless dress in satin is the basic ingredient in a variety of party-clothes recipes.

Pair that dress with chandelier earrings, an evening clutch bag and strappy sandals and you have an outfit appropriate for the fanciest occasions, says Seymour, but that same dress ” sans earrings ” and wear flat shoes and carry a black crocodile-skin bag and the outfit fits dinner in a restaurant or an at-home party.

Seymour also says the black dress is a wise investment because, if you attend only a few fancy events a year, the dress can be recycled each time with no one but the wearer knowing it’s a repeat performance.