Get a simple black dress that leaves your arms exposed and rises a good few inches above the knee. Dresses that have white classic collars or even some lace and ribbon in a baby-doll dress fashion also work, as long as most of the dress is black.
Find a pair of Mary Jane shoes either in black or white. No matter which color you go with, or even if you go for an unorthodox color like red, wear a pair of black tights with the shoes.
Keep your hair dark and your bangs low and straight as a razor. If you feel the need to add a little color, then a streak or two of blond or platinum will keep you in the Emily the Strange style.
Stay quiet and to yourself around others and don't be afraid to appear a tad antisocial. When you interact with others, use some dry, dark humor as you generally distance yourself from liking most things.
Associate with black cats, which are a trademark of Emily the Strange's character. While Emily hangs out constantly with her four black cats, a black cat patch or photo is enough to keep yourself in Emily Strange style.