According to psychologist Leslie Zebrowitz of Brandeis University, you judge a person by reading four facial cues. Her research, published in Current Direction in Psychological Science in June 2017, these are the four cues: 1. Babyfaceness. People with "baby faces" will have large eyes, short chins, round faces, and large foreheads. Seeing a more baby-like face could make us treat that person more kindly, given our evolutionary soft-spot for youngins.
2. Familiarity. People like what's familiar, so seeing a familiar face is preferred. Don't believe it? This experience even happens for babies.
3. Fitness. There is a general understanding about what features we find attractive in a face, and healthy people look attractive. When we see a healthy, fit-looking face, we see someone who's likable, intelligent, and capable.
4. Emotional resemblance. Humans are pretty good at reading emotional expressions in the face, so we're going to pick those up right off the bat to try to judge someone. For instance, low eyebrows will make someone appear angry. An up-turned mouth will make someone seem happy, regardless of how they really feel.