To describe a beautiful girl, use words that focus on the aspects that you find beautiful about her.These descriptive words, known as adjectives, serve as good ways to point out what features you find beautiful in that girl.
Describing a beautiful girl can range from being very detailed to simple. For example, saying a girl is beautiful because of her long hair serves as a great description, but it can be taken a step further. You can say that a girl is beautiful because of how her long blond hair moves in the wind. The previous example doesn't just describe the girl's physical appearance, but goes into greater detail of why the girl's long blond hair is beautiful.
Describing a girl's beauty isn't subject to just physical appearance. Other aspects can be considered beautiful based on the observer. Saying something such as, this girl is really beautiful when she looks at you and smiles or she sings beautifully are both good ways to describe someone's beauty that goes beyond simply how they appear.
Other ways to describe a beautiful girl involve noting the clothing and accessories she is wearing and pointing out how it accentuates her beauty or makes some of her more unique features more prominent.