Knowing the different nonverbal cues that people give off will give you insight into what others are truly thinking and feeling. Recognizing when somebody is nervous will help you to see when someone is romantically interested in you or even when someone is lying to you. Also, knowing about body language will help keep you more aware of your own body and the signals you're giving off to the world.
When trying to see if someone is giving off cues that they're nervous, pay attention to several different body parts and movements. Take note of their face and how they move their eyes, eyebrows and mouth. Notice how they move their head, shoulders and hands, as well as how they sit or stand. Also, how a person places their head and feet can give off nonverbal cues. If a person seems to be twitching and fidgeting, they may be trying to hide something. When a person is nervous, they'll try to take up less space with their body -- their shoulders will be hunched, their elbows will be pulled into their sides and their legs will be together. Touching the face, wringing their hands and shuffling feet are giveaways that someone is nervous.
Pick up on the cues that a person gives off that they're on the brink of having a nervous breakdown. Someone who is close to the breaking point will keep their shoulders hunched. They may have a blank look on their face, fidget and get irritated or sad easily. They also may have severely gained or lost weight.
You can decipher if a person is romantically interested in you or not by paying attention to their body language signs. When someone begins to feel an attraction to another person, they'll give off subtle, nervous cues that communicate that they're feeling butterflies. If you make eye contact with someone and after a few seconds that person looks away, they could be nervous, but in a good way. If they fidget with their clothing, touch their hair and face or play with their hands, this means you're making an impression on them.
When a person is lying, they'll often exhibit nervousness because they know they're doing something wrong and they don't want to get caught. While some people are better liars than others, the act of knowing you're saying something untruthful will ultimately cause unrest in everyone. Stuttering, speaking in a monotonous tone and saying "Um" a lot while speaking are cues that a person may be lying to you. Sweating, blinking, not being able to make eye contact, scratching and touching the face are all signs that a person may be lying to you. Also, changing positions a lot points to someone being anxious, sometimes because they're being dishonest.