Before choosing a haircut, you need to know the shape of your face; even the simplest style could wreak havoc with your look.
oval
Favors you: All! You are lucky because any style fits perfectly with the shape of your face. Your forehead and chin are practically the same width so your face looks proportional. Most models and movie stars have an oval face, and as you may know, almost any haircut suits them.
You should avoid: Nothing, any style that catches your attention will go perfectly with your features.
round
It suits you: A haircut that can lengthen your face. Chin-length layers, long, asymmetrical fringes, and full-length hair are ideal for a round face like yours. It is very important that you look for styles from the chin, otherwise you will only give volume and fatten your face more.
Avoid: Very short cuts like the ‘pixie’, straight fringes and ponytails that show your whole face; If you want to pick up your hair, we recommend you make a high bun, leave some hair loose and have an asymmetrical fringe.
square
Favors you: The long haircut that softens and frames your face. We recommend leaving your hair at shoulder height or lower with a fringe that can be divided. You can also soften your jawline further by having long layers that start at your jawline.
Avoid: Very short haircuts will only make your face look even squarer.
Heart
Favors you: A wavy, Chinese and soft style that can highlight your features well. The ‘pixie cut’ that several artists have adopted will also look perfect on you as long as you can add dimension to your hairstyle. You are one lucky girl because long and short haircuts look amazing; even with a fringe as long as it is long.
Avoid: The haircut that ends before your nose or that simply does not serve as a frame for your face. Those that accentuate your forehead and not your chin, forget them!
Diamond
Favors you: Almost any haircut. A very daring one, above the shoulders and with long fringe. You have no problem with a wavy or Chinese style, but we recommend a fringe that can soften the upper part of your face a little.
Avoid: The layers in excess or those cuts that give volume to your face like the short ones. Better opt for something long to give proportion to your face.
Related note: Questions and answers about hair care, here.
Source: Twentysomething