Shirts: Wear good quality shirts, in preppy colors. You can also wear brightly colored shirts, but try to team these with a pastel. Pants: Own about two pairs of dark wash skinny jeans and jean shorts (depending on the weather). Have at least one pair of khakis and a few patterned pants in stripes, plaid, etc. Shoes: Own a pair of brown riding style boots, Toms, Uggs, loafers, topsiders, canvas shoes, flats, or fuzzy boots - any of these shoes will be great. Have one pair of good quality tennis shoes too.
Don’t forget the hair. Have pretty hair bows in pink, green, and/or navy blue, use these to tie your hair up in a high ponytail or pigtails. It is also cool to get bows in your school/team colors.
Join lots of school clubs. Run for school president or for other officers.
Speak a language. Consider taking French at school and learning Italian, German, or Spanish in your free time. Learning any other language is good too. Latin helps as well. Take Chinese and ace it.