Read books on body language.

https://www.amazon.com/Emotions-Revealed-Recognizing-Communi...

https://www.amazon.com/Unmasking-Social-Engineer-Element-Sec...

For anyone interested in becoming more cognizant of body language/non-verbal communication, check out Chris Hadnagy's Unmasking The Social Engineer[1]. It will make socializing or just people watching far more interesting and engaging.

[1]https://www.amazon.com/Unmasking-Social-Engineer-Element-Sec...