Most people when they start trying to learn mentalism or psychology become obsessed with body language.
For those of you who don't want to read (lol what are you doing here)
here are the basics:
1) Typically, there are only comfort and discomfort signals.
2) No one action indicates any one specific emotion ( folded arms don't always mean defensiveness!)
3) The change in body language is more revealing than body signals (Did someones body shift after you said or did something?)
4) Look for multiple "signals" to establish what someone is thinking. (Oh hey! That person is smiling, nodding, and leaning in to hear what I have to say. They must like me.)
5) People are suppose to be expressive. If someone is not expressive (if they are normally) they are most likely uncomfortable.
6) Just because you know someone is uncomfortable you technically might not know why they are uncomfortable. (Asking if they are lying is an uncomfortable question. They could be reacting to the awkwardness of the question OR they could feel awkward because they truly are lying. You honestly have no idea. Unless you really can read minds, don't jump to conclusions. :) )
Those are my tips. If you actually DO want to learn more. I can't recommend Paul Ekman's work enough. He has a class on micro-expressions and his books have been invaluable.
https://www.paulekman.com/
Paul Ekman books:
Telling Lies
Emotions Revealed
Another great one is:
What Every Body is Saying by Joe Navarro
Very simple but extremely practical.
Please don't accuse people of being liars. They might be... but saying, " Hey you're lying!" usually doesn't help anything and makes the situation worse.
That's all for now.
-Brad