Also, if there are people who gesture's give away too much they may try to restrain themselves as gesture verges on an involuntary action. Gesture's cousin and sister to involuntary actions. We rely on expressions a great deal, but we rarely think of them. A smile, a frown, a snarl can say a great deal. Some may be deliberate, some may not be.
Humans are very facially-oriented.
Indeed, one of my hobbies is learning to draw, and I started with the human face. Keep in mind how characters in your world regard and use expression, and much like gestures, take a look sometime at people communicating and notice the role it plays. Clothes say a lot. Maybe you can't judge a book by its cover, but clothes can be used as tools of communication. Casual clothes may say you don't care or that you're relaxing.