How does one get better at/practice reading people?

Humans give off a lot of data about their thoughts and intentions without speaking. Facial expressions, body postures, and even movement patterns reveal information that's not exactly the easiest to pick up. I'd like to say I'm half-decent at interpreting personality and intent via 'reading', but I really have no clue because I don't have anyone to compare to.

It seems like an immensely important skill to have, especially if one works constantly with people they don't know. Practicing or otherwise improving said skill seems to be quite difficult.