When one dreams of another person, this does not mean that the other person was also dreaming of him. However, depending on the context of the dream, the appearance of the other person can mean a few different things to the dreamer himself.
Dreams are symbolic. This means that the people in your dreams are also symbols of things going on in a person's mind — not necessarily the real actions of people he may know. Because dreams are tied to the subconscious mind, they are able to reveal different parts of people that might not normally be revealed.
One way to gain insight into the appearance of a person in a dream is to consider the full context of the dream — not only the person who appeared in it. For example, if one dreams about his best friend from high school, he should consider the life experiences he shared with that friend. Was there something that this friend inspired him to do?
Those who attempt to dream of a particular person can attempt to think of that person or an experience with that person, but this is not always successful in inducing a dream. It is the subconscious that brings these people to the forefront of dreamers' minds.