Do you know what oily looks like? THIS:

Trust me, you don't want to look like you just dipped your face in your frying pan. The purpose of going for the "dewy look" is to give your skin the natural sheen that makeup-less skin has.
THIS is dewy (and flawless, might I add) skin:

Scarlett Johansson often has a classic, natural, dewy makeup look. You can achieve a simplistic dewy look achieved by using creams and liquids instead of powders; usually a cream or mousse foundation would be better for girls with oily skin (to still keep the skin's oils from getting too out of control) and a liquid foundation would better suit someone with dry skin (like me). To avoid your face from getting oily later in the day, you should brush on a sheer powder all over for sealing the cream/liquid makeup.
In an attempt to achieve a contoured look (with shadows and highlights), many girls end up looking oily or too shiny. So how do you highlight without looking all shiny? Perhaps it's just because she IS gorgeous, but Hilary Duff looks amazing and flawless in this photo:

The highlights on her cheekbones, forehead, bridge of the nose, and chin are all in the right spots and serve their purpose: to contour the face.
Well, I hope you girls learned something from these small tips :)
Stay tuned for more from Beauty!
XO,
The Brat