The available information
First and foremost, you can learn about the man his surname, name and patronymic, year of birth and place of residence. One is enough for that conversation. You can learn about the Hobbies, about the friends and relatives. Such information can be obtained even when as if they were ordinary acquaintances. Pretty easy to learn an interesting person, what kind of music he likes, what movies, what programs. It would also be useful to find it in social networks. All this will help for further investigation so that the resulting data better to write down somewhere.
Information from sources
More recently, to obtain hidden information only to law enforcement agencies, and now unlimited Internet access allows you to get a lot of information. In social networks people spend a lot of time, leaving information about yourself. Locate the desired person in all social networks and read information about it. It is also worth to see pictures and videos of the person. It is possible to learn about the Hobbies of the person. Also, scrolling through the wall, you can find a lot of useful information. Worth to watch and friends list, and prefer to focus on the most popular. It is likely to be one of the best friends. Try to mingle with friends, learn some information. But don't push too hard, ask a lot of questions. Otherwise it would be like to investigate.
If possible, you should turn to the man's neighbors. This is especially true of grandmothers on the bench in front of the house. But there is already information might be slightly exaggerated. But you can see that there is a person in the home.
That same person can tell himself unconscious
On the nature of man and his manners can be learned by mimicry and gestures. But to accurately understand body language, you need to study a lot of literature. But then when dealing with a person can read the information in his gestures, like an open book. To find out what he wants to say, where is lying, where is sincere. As they say, body language can not lie.
Another interesting way is to introduce a person in an extreme situation. Scientists have proved that in a state of stress and shock a person shows his true nature. Take him skydiving, Canoeing, or even on any extreme ride, and watch its actions, emotions and reactions. During the adrenaline rush of the man completely open.