This post is made upon the request of my friend despina who was asking me what clothes to wear so her waist look narrower. There are some tricks which i use too, even if my waist is well defined, because with some of them you can hide your tummy!!
The perception of your waist is determined almost entirely by the clothes you wear, so you can emphasize, and even create, a narrow waist simply by picking the appropriate clothes.
Draw attention to your waist with belts and dresses that pinch at the mid-section. If you have a straight shape, this is a must because it'll create the illusion of curves. If you have a pear or hourglass shape, this will accentuate your existing curves.