Although black will give the appearance of sleekness, you can use other colors also in a way to elongate you body. First of all, choose a monochromatic outfit and then add some contrast with an overshirt or cardigan. The cardigan or jacket needs to be left unbuttoned to create that vertical line down the front.
Scarves too will add to the look. Leave them hanging long in the front and tied loosely. Your skirt, shoe and pantyhose or tights should all be the same color. No chokers though, they will not do, instead choose long necklaces and top with V-necks. When picking a skirt, is should be longer than it is wide to again give a long look and high heels will add to the effect. The higher the better.
With all this similar color, don’t let it get boring. Use textures like leather with knits. If you are a small person, pick prints that are small also and balance it all out, meaning not everything must be long. For instance, pants with a short jacket or maybe when you wear a shorter skirt, compliment it with a longer coat.