Cocktail dresses are always in style, but you have other options.
What to wear: These days, a cocktail party can be anything from a swanky society affair -- cue that glittery knee-length number from the "special occasions" department -- to a low-key group of friends gathered around a platter of crudités. But for the most part, "cocktail parties are dressy-casual, so you can't go wrong if you wear a top with some special details and a skirt or tailored pants, plus heels or fancy flats. Avoid fabrics that are too casual, like chino, jersey, and denim."
A fitted cashmere or fine-gauge merino-wool top with a knee-length satin skirt, heels, earrings, and an armful of stacked bangles or a somple short gawn is just right. Also a pantsuit doesn't look too corporate. (Under the jacket, wear a silky camisole or some other feminine top with an evening vibe.) Keep in mind that different cities have their own dress codes, Cocktail attire in lagos is just as dressy and chic as in jos, regardless of the weather differences, while in abuja it's interpreted a bit more casually, because the city is relaxed."