COLORS

As we said above, try to bring different types and colors of your outfits. Ideally, bring at least one dark, one light/pastel or white, and different colors. 4 different colored sweaters & levis isn't really giving variety. Neither is having different types of outfits, but all of them in the same color - you won't really see the variety as well.
Want to Look THINNER?
Hey, not even Brittney Spears has a perfect bod - what you wear can make a major difference in your size appearance in your portraits. A few suggestions, for those who want to look better!:

Light & bright colors (yellow/red/pink/white/etc.) will make you look larger.
Dark, cool colors (blue/green/brown/grey, etc.) will make you look smaller.
Solids Only! - NO Stripes, polka dots, prints, etc.
Long sleeves are a definite plus - avoid sleeveless outfits, unless you've got great arms & elbows. This is especially true on your formal & semi-formal outfits.
The point is to draw less attention to your body and more to your face - that's what it's all about!