It's as easy as looking at your skin tone. To make matters simple and understandable, the skin tones are classified in four categories. Fair, golden, bronzed, and dark. Pick the tone you are closest to, and find the right colors for you.
Choose light colors, like beige, sea-foam, rose, and other pastels. Creamy colors with a hint of peach work wonders. However, don't limit yourself to hues as fair as your skin. Mix a bright and colorful piece, (like a turquoise polo, or bold headband,) with a more subtle color. Girls with dark hair and porcelain skin look absolutely stunning in rich purples, emerald greens, and deep reds. Avoid blacks. They will make you looked washed-out.
Golden skin really is light skin, but it's a few shades darker than fair, and it doesn't look like you're a porcelain doll. Any color looks gorgeous on you. In the daytime, try colorful pieces. Also, sage green pants look great. For evening, go with subtle, yet powerful hues, like a kelly green dress, or a girly pink. Any shade of blue looks beautiful too. The best part? You get to wear black, the most slimming, simple, and intriguing color of all.
That beautiful, I-just-got-back-from-Hawaii skin. Turquoises, oranges, and pinks look best on you. Any color that's a mix between two others is key. They play up your tanned look. If you dare, try a shade of red, and steal the spotlight.
Your type of skin looks beautiful against semi-rich colors. Avoid very dark colors. Plums, ruby-reds, and forest-greens look amazing. For a noticeable contrast, mix in an ivory piece. It makes your skin noticeable and is very flattering.