First of all you must be honest with yourself! In general you will want to accentuate your best features and minimize your least favorite when choosing a hairstyle. For instance if you have larger forehead than you might want to have bangs, but if you have the most beautiful eyes than you dont want to cover them up with hairstyles with long bangs.
Look at your face shape! Hairstyles for rounder faces would normally be longer, possibly shoulder length hairstyles, to minimize the width of your face. On the other hand a hairstyle for a longer faces could be shorter with bangs with hair flipped outward to give your face a wider appearance.
No matter what hairstyle you are searching for, the next best advice we can give is look at our many hairstyle galleries or celebrity hairstyles and find pictures of women with similar face shapes and features.