Sometimes it helps to just let go. Portrait photography can be too serious and it helps loosen you up by showing your goofy, funny self. If I don’t have a lot of time to get to know someone I ask them to show me some crazy. Make a crazy face. These photos are rarely seen except by me.
Faces are strange. They contain so much information. But a person who can find their inner clown shows me their humanity. And it’s humanity I seek to convey.
A person who’s not afraid to show this side of themselves can often show their other, more serious side too. We’re all actors, whether we’re aware of it or not, and posing for a portrait is just another act. It’s just a matter of holding an emotional state in your mind and sitting still.
So whatever it is you want to convey in your photo, think it, be it. Confidence, approachability, friendliness - it’s all in your repertoire. The face has evolved to communicate. Use it.