Your mien is how you present yourself, the impression you make. It's best to keep a low profile but a dignified mien.
The source of the word mien is not completely clear, but it does involve a French word for "facial expression." A person's mien is a look or quality that tells a lot about their personalities or temperaments. A person with a cheerful mien probably radiates happiness and energy, while someone with a serious mien may have an air of being lost in thought.