As a person with Asperger's syndrome, conversations and body language are not naturally something I understand. I learned most of what I write about through movies and books. Watch an emotional movie, as well as reading well-written books. Watch the characters interact. Can you tell when somebody is lying? What about when they're happy? What do they do? Sure, they smile, but what else? Do they stand a little taller? Relax a bit? What about other emotions. Sadness, for example. People don't just cry when they're sad. They could bite their lip to keep it from trembling. They could refuse to meet somebody's eyes. They could be slouched over. Their voice could crack.
Also, sometimes dialog by itself can convey emotions. Exclamation points can indicate deep emotion, too. Excitement, joy, anger, it can be there. Subtle is good, too. If you think your readers will understand without description, go for it, but if you need to describe, try expressing it through action. Hope this helps.