Start with Body Language

Be very careful. Over the years I married two women (at different time of course). Both very beautiful, elegant, Dangerous and Mad. James

Everything and nothing. It's pretty much what @resserts says. What I find interesting is when someone is in a relationship or married to someone for decades and there is still something they don't know about them. Like when I see some story about someone saying, I never knew that he had an attraction to men, or I never knew he was a murderer. Were you paying attention? Lol

But just to add to my comment above. My own intimate relationships and friendships are not the same as observed interactions of others. My own relationships involve more of my own interferences than observations do. Or do they?

It all depends. Some people are good at observing people and reading gestures, body language, etc... Some people want to be good at that but they are not necessarily.

I find that the best way to see what someone is like is to see how they type. Is the person eloquent or just running on automatic? I prefer to talk to somebody who's got the good up top.

Even better "how many observe and then project their traits on to the observed". I will never forget an ex catholic school teacher turned security company operative who because of my nationality, occupation, divorce, parenting of my daughter seemed to believe that I was a thief and he was going to prove it by hook or by crook. I would discover him stalking me in the supermarket to catch me shop lifting. He set up that I relief someone on the door to collect the last dinner fees at the Lions club weekly meeting having counted the collected money and planted marked coins that identified someone had made an unreceipted donation of their loose change or the collection was baited. I was finally black balled and banned for life from Lions Clubs world wide because the committee had run out of money and wanted me to illegally pay money from a charity raffle that I was trustee for and refused. Instead charging the charity legitimate and accounted for expenses which were then paid into the Lions bank account as dues and fees that I owed thus saving the committee the embarrassment of being investigated for charitable fraud. It was only after the security guy died of I suspect a brain tumour that his wife told the Lions what he had been up to. Although they verbally apologised they never got the record at Lions HQ corrected. ... Bunch of knife and fork ignorant weak hypocrites. Observing them warned me that something was amiss. Unfortunately for me I've never had any skill at playing politics and so don't, to frequently having to walk away from stupidity and narcissism at the expense of appearing wrong.