The key characteristic of a round face shape is that the width of your face is roughly the same distance as the length of your face. On one hand, with such a face, you need a long hairstyle with layer on the top. You'd better try your best to keep your hair longer than the chin because it can naturally help you lengthen your round hair shape. Layer the top and keep the rest of your hair relatively close to your face also can make your face appear longer and narrower. At the same time, such long layer hairstyle needs more volume on the top of your forehead because it can make your face look longer and beautiful. On the other hand, there are a lot of women prefer short hair, round face women are no exception because short hair easy to manage and style. For those who love short hair women with round face, you should opt for a swept back style and also add volume and height at the top of the head through a series of layers or heightened bangs which can make your face appear longer and slimmer.
Remember to stay away from curly hairstyle because it always keeps away from your face which can add volume to the side of your face and make your face look wider. But if you are naturally curly hair, you may try your best to keep it longer. Also you should avoid short crops with straight bangs in front of your forehead, which only add weight to a round face. Bobs are also should be avoided because they emphasize your round cheeks.
These are general and useful guidelines for you can follow. Try your best to find a style which suits you best and can show your beauty side.