Reading Body Language, Facial Expressions, Eye Contact, Smile

Facial expressions can be very difficult to read. People smile for a wide variety of reasons:
1) They are genuinely happy to see me
2) it's the polite thing to do
3) They do it all the time and it means nothing
4) It's a mask.
5) It's a ruse, deceptive they want to manipulate. They need something or want you to do something for them, possible sinister

Eye Contact
Eyes have "expression" that can be almost too intense. It is highly accurate in dictating how someone is feeling about themselves, about you and their life in general.
I see the eyes of someone in pain and it hurts me.
Likewise, with people who are upset or angry with me, painful.
I've seen "dead eyes", an expression completely devoid of any warmth or care; otherwise known as, "You are dead to me" or "I feel nothing at all for you."
Happy, warm, "I like you" eyes are my favorite.
It's easy to tell when someone is uninterested and bored. Those persons who look a away from me...I find upsetting and rude. (Yes, this from someone who rarely maintains eye contact. I deplore double-standards, but it is true)
While I cannot routinely be accurate in reading facial cues, I'm actually very good at reading body language. My Aspie brain easily picks out the detail of small and slight movements, shifts in head tilt and subtle foot taps.
The way a person carries themselves, that unique walk tell me about the overall happiness and well-being of an individual. How free are the major joints? Do the arms swing casually from the shoulder carefree? Or are arms pressed tightly to the body in defense and pain?
The ability to determine who a person is, even from a good distance, is one of my hallmarks. Each walk is very unique.
I guess I entered into this subject because of an event this morning. I went to my doctors to ask for copies of some of my medical records. My intent was to procure three or four different pages, but upon my inquiring at the reception desk, it was quite clear the secretary was having an awful morning. Without her even speaking, her eyes looked tired and heavy. Her shoulders were low, sank, in futility and exasperation. Her arm movements were slightly erratic in confusion, frustration.
I could see that I was an imposition...that my being there was at a hectic time for her.

I respected that, pared down my request to just two pages and left.
Reading people, faces, posture, movement is a valuable skill. It makes people, the world, a little more predictable.
I do recommend that if you would like to learn how to read body language, there are many very good and easy to understand books and material on the Internet. I read a number of them whilst a teen and believe that they helped me.