If you can understand a man's body language, you will gain valuable insights into what he is thinking about you. You will be able to tell if a man is interested in dating you, wants a fling, is hoping for a friendship or if he has plans for a business type of engagement.
Know a little about the man whose body language you are interested in reading. Do your research. Before you go thinking that you can figure out everything about a certain man by a general book, you might want to find out about the specific man first. The book might tell you that a man is not interested in you if he is fidgeting around while talking to you. However, you might find that the man you are interested in happens to be incredibly nervous around women, and that he fidgets more when he is interested in a woman.
Learn about the man's culture. In some cultures, there are different meanings attached to nonverbal cues. A Native American man may not look you in the eye, for instance, but this doesn't mean he isn't interested.
Realise that the place where you have the encounter with the man may influence the body language. If you are at a formal gathering, and the man is the guest of honour, all eyes are on him and he may be somewhat guarded in his body language to you. If you meet at the park, however, the man may be able to display all of the body cues available.
Know that your body language can affect a man's body language. For instance, if there is a man interested in dating you, he might come up to you with a big smile on his face, showing his interest. If you're in a bad mood and you scowl as he approaches, he may not display that same smile if he thinks you aren't interested, or if he senses it's not the right time.
Read the man's body language. The man either wants a business relationship, a friendship, a fling, a dating situation or no relationship. You have to know the cues for each one. If the man wants a business relationship, you will get a formal firm handshake as you greet. There will be directed eye contact, usually at the end of phrases. The man will keep a distance from you, but will be facing you as you talk. A man interested in friendship will make eye contact, but of limited duration. The man will turn toward you sometimes, but not throughout the entire conversation. The man will seem interested in what you say when you talk about normal subjects like sports, and there will be some smiles, but not ear-to-ear smiles.
Look for the big smile. If the man is interested in a fling, he will get too close too soon. He will come right next to you and may seem to invade your personal space. He will keep eye contact too long for comfort, and may touch you even though he doesn't know you. Expect him to stroke your face lightly or to play with your hair. The key to the fling is that you will most likely feel uncomfortable and the man likely won't respect your boundaries. If the man is generally interested in dating you, he will turn toward you during the conversation. He will look into your eyes longer than a friend would but not as long as the fling guy. He will have big smiles that show he is generally interested in the conversation and in you.
Remove distractions. If the man has no interest, look for signs of fidgeting. The man may look away frequently or shuffle his feet from side to side. He won't be smiling and he may have his arms or legs crossed. Just understand that some men are distracted easily, so if he starts watching television or a passer-by, this doesn't mean there's no interest. Remove him from the distraction and see how he responds at that point.
Read the body language over time. If at first you can't gauge a man's body language, wait until the next encounter. You will generally see a pattern develop in how the man reacts to you, and your accuracy in gauging his nonverbal responses will improve the more times you talk to him. (His interest could also grow as well.) You could have caught the man in a bad mood or with something pressing on his mind the first time.
Realise your own preconceived notions of men and how this could play into how you read the man's body language. A long gaze showing interest could come across to you as staring, if you think that all men just like to stare at women. Reading body language is not perfect science. A person might have vision problems that don't allow for eye contact, or someone might have an anxiety disorder that makes them uncomfortable looking you in the eye. There is no way to know every possible thing that could interfere with reading body language correctly.