I don't know how I do it. I just do it naturally.
On many occasions, I have had people tell me I understand them better than they do themselves, even with modest contact.
Motives and honesty scream at me. Fears and concerns pop out as well.
I try not to read everyone I meet, but even without trying, I can see into people and figure a way to make their life better.
It gets overwhelming at times, especially with large groups.
So, how do I do it? I don't know. Am I right 90+%? Yes.
Can't all INFJs do this?