Conveying specific emotions
A tense character will be a little hunched and have uneven shoulders, because the body is gearing up to have to either protect itself or run. The jaw will usually be clenched and the eyes wide. I emphasise this by making the iris/pupil a little smaller. There might also be a hint of disgust in their expression, to suggest their sense of nauseous anxiety.
Laughter is often involuntary. While a person in the throes of hilarity may make themselves more prone by leaning back and dropping their shoulders, the body will sense its vulnerability and often try to shield the face and vital organs with the hands. Nostrils will flare; the fat of the face will converge around the eyes; and the teeth and gums will be on show.
When your character is exhibiting an aggressive emotion, such as rage, the head and hands will typically be projected forward. Tendons and muscles will be tensed and the lips curled inward to bare the teeth: these are primal intimidation tactics. Be careful not to exaggerate the mouth too much though, as doing so can dehumanise the character.