Watch cable news. Since they are all news all the time, they have a variety of guests that provide ample opportunity for viewing different people and their body language.
Tune into MTV. Their reality shows usually have eccentric characters and they’re typically younger than the cable news’ guests. Besides their body language, listen to their speech and note how they are dressed.
For the fun of it, watch a TV minister. They are frequently dramatic with bouts of weeping, kneeling, shouting and even fancy footwork.
Observe your own family and friends. How do they walk into the room? Do they shuffle? Stride in like they’re on a mission? Head held up or down? What do they do with their hands? How do they sit? Where are their feet? Are they kicking you?
Consider having your characters interact with their environment. You can manipulate the setting, so they can touch or move something that is important to them, distressing to someone else or heightens the plot.
You can also influence how the reader feels about a character through body language. Suppose you don’t want the reader to like the character, you don’t have to give him negative personality traits (abusive, rude, ill-mannered, etc.) which could be cliché.
Give him disgusting body habits: he eats his own ear wax, picks his toe nails at the dinner table or sneezes on his hands and then wipes them on the furniture. Gross, right? I’m immediately detached from this character just from writing it.
For writers, researching body language is easy. All we have to do is train ourselves to watch people critically.