In general, the best haircut for a long face is one that helps to shorten the face. This does not mean you absolutely need to choose a short haircut, but some shorter layers around the face might be a good choice. Searching online for haircuts that appeal to you, or looking in books and magazines, may be a good way to find sample haircuts to bring to a hair stylist. There are also numerous websites that may allow you to upload a photo, and then "try on" different haircuts without making any actual changes; these can be a great way to help you choose the best haircut for a long face.
By definition, long faces tend to be narrow as well, which is another reason a long haircut without any layers may not be the best choice. This can make the face look even longer and narrower. A heart-shaped face, which is characterized by a narrow chin and a widow's peak on the hairline, may be slightly more versatile, but will make it virtually impossible to part the hair in the middle. All of these things should be considered when trying to choose the best haircut for a long face.
People who have clearly defined features often find that a very short haircut for a long face looks nice. For women, this may be a bob, in which the hair is cut to chin length all the way around the head; this style works very well for straight hair. People with thicker or more textured hair might find that a pixie cut looks nice, with the hair cut even closer to the head. Corresponding styles exist for men as well. Individuals with curly hair might find that a shorter layered cut has the same effect, and helps to frame the face in a flattering way.
In fact, layered hairstyles are some of the most popular options when choosing a haircut for a long face. These look great with straight or curly hair, and can allow you to still have longer hair with a few shorter pieces around the face. Bangs, whether they are blunt bangs or side bangs, can also be combined with a layered haircut to be especially flattering on a long and narrow face. Keep in mind that it is much easier for a hairstylist to create the haircut you want if you know exactly what you are looking for, or if you have a sample photo, so spend some time looking around in magazines or online to find a clear example to be sure you get a great haircut.