TL;DR
Harsh overhead light, squinting, arms-crossed posture, and busy backgrounds can all reduce approachability even when your intent is friendly.
Lighting and angle
Front-facing soft light flatters most faces. Strong top light creates shadows under the eyes and reads as tired or stern.
Expression and posture
Crossed arms, turned-away shoulders, or a tight smile can signal guardedness. A slight body angle toward the camera often feels more inviting.
Background simplicity
Busy scenes compete with your face. A clean background keeps attention on expression and eyes.