If you don't know the dress code, keep simple. If you're afraid of being overdressed, understand that casual is not its opposite. An minimalist slip dress is an elegant option that won't run the risk of looking overly fancy or informal. Adorn with jewelry and statement accessories for extra glamour—you can always remove and stow them in your purse if need be.
Choose the right fabric and styles. We rarely say this, but consider your comfort level. Parties are as much about the socializing as they are about the style, and if you're not at ease in your ensemble it will affect how enjoyable your evening is.
Consider the accessories. That is not really the case, you may want to choose a contrasting color to compliment rather than match. Some accessories might be too flashy that they totally change the look of the dress. You must always be aware with the number of colors the dress can be worn with, whether it can be worn with gold or silver jewelryand even the type of shoes that can be worn with the dress.