You'll see a few tips and tricks that are useful. Like when a person crosses their arms, they generally disagree with what you are saying, etc.

The most important thing is to pay less attention to the content and more attention to the tone, stance, demeanor, circumstances, likely self-interest in the situation, notice the little things everywhere and that will give you a clearer picture of what you're dealing with. Do this often enough, over and over again, and it'll become second habit.

Content is rarely useful unless you're engaging in a very data heavy conversation, like for example you would when describing requirements for a project at work. During regular conversation, everything is generally geared toward communicating emotional state, so focusing too much on content dulls your senses and you don't pick up what you need to pick up.