A classic option for a cocktail dress is basic black. A dress like this by Jean Paul Gaultier can be worn with a cardigan and low heels for daytime. And then for evening, off goes the sweater and on come the stilettos. A length that hits below-the-knee looks great with super-high heels; with a shorter hem, you'd want to stick with a lower heel.
BUY A DRESS LIKE REESE'S Matte jersey tube dress, Chaiken, $178; bluefly.com.