The absolute easiest way to look your best is to dress to flatter your particular body type and wear that style of clothing exclusively. It doesn't matter what size you are -- it's all about dressing to compliment your shape.
If you're shaped like an hourglass, wear clothes that hug your curves. Avoid loose blouses and dresses; they'll make you look bigger than you are. Think belts that cinch your waist and tailored blouses. If you're shaped like a triangle (smaller on top, bigger on the bottom), wear clothes that pull the eye up to the most slender part of your body. Think bold tops and statement necklaces, with dark, sleek pants. If you're shaped like an inverted triangle, you want to elongate the torso by wearing drop-waist dresses, skinny jeans, untied scarves and long necklaces. If you're shaped more like a rectangle, you want to create curves. Wrap tops, draping, and bias cuts help create the illusion of bust and hips.