Study the face, observe the body, read the person

There's a lot you can learn by really looking at the person you are speaking with, whether in person, on a zoom call, or even just with audio.  We all send dozens on unconscious or subconscious cues with anyone we're communicating with each moment.  Depending on an individual's own self-awareness and their awareness of these universal signals, the messages may be much more subtle than others. 

Here's a few rudimentary and especially 'loud' cues.  Someone has their arms at their sides, their shoulders comfortably back and relaxed, they are turned slightly towards you and leaning in a bit - this person is sending a cue of being relaxed, trusting, and interested actively in what you're saying to them.  Now, a person is caved in (their shoulders are in front of their rib cage so their front side looks sunken un), they are looking down and/or avoiding eye contact, they're feet are crossed.  They feel insecure, uncomfortable, untrusting and want to avoid this interaction. 

There are many ways to learn about all of these cues.  You can find them in books or YouTube videos - and you can sharpen your eye for them by watching police interrogation videos or just really top notch actors in theater, TV, and movies - since they have to know and emulate these behaviors to tell a story effectively.

It's advantageous to be aware of these cues because it can greatly improve your ability to be a good friend, family member, and co-worker as you use the physical cues to add a richer subtext to what's being communicated.  It's also good for your own self-awareness of how you're presenting yourself and what you're communicating despite or in addition to the words you are selecting to say.

If you want to dive deep and get really good at this, take an acting class  (and trust me no one cares if you aren't an actor or don't want to be one - if you pay, you're welcome).  An acting class that deals with the body, movement, improv, doing blindfolded work, space work, these types of things.  This will get an understanding under your skin of how to read and respond to these cues that any and all people put out there.  If you want a more introverted option, a great book to start with is 'What Every Body is Saying' by Joe Navarro, a seasoned FBI agent and expert is ready body language.  He's also one of the guys the great Netflix series 'Mindhunter' was based on, just a fun fact, you're welcome.