Psychology is a huge subject with a lot of different fields of study (like social psychology, personality psychology etc.). However, there is a basic concept that is relatively easy and can help a lot in your psycho-analysis of people.
People, in most cases, reveal their thoughts by doing things they are sometimes not even aware of. Say, lying. People who lie often touch their ears, nose or mouth after or during a lie. Mostly, they aren’t even aware that they’re doing it. You can also get an idea of the person’s state of mind and feeling of social hierarchy by what he or she is doing. If you feel threatened, you will make yourself smaller by holding your limbs closer to your body. Also, you’ll likely lower your chin or raise your shoulders and put objects between you and your supposed opponent (even something as small as a glass). You are doing this to protect yourself if the situation comes to a fight (even if it is a situation which would never go there, your body still reacts in this way to a perceived “danger”).
If you’re feeling superior, you will be relaxed (i.e. leaning back, with relaxed shoulders and loose muscles etc.) and likely you will expose your throat to show that you are not afraid.
There is a whole range of studies on this very subject, including micro-expressions and other body language things. However, the main point to remember is that minor behaviour is very often key clues in what a person is thinking. Look especially at the eyes, the face and the extremities (i.e. feet and hands). You can figure out what a person is thinking not by what you know, but by what he's telling you.