I have a question? What if you try so much to know better about a person but the person in question doesn't want that. What if (s)he is keeping away important details from you? How then do you go about that?
Remember, you can't force anything out of anybody. You only know what they want you to know.
Your last statement
Since the only way to know more about people is for them to tell you, you can make them want to tell you more about what they want you to know. Everybody will talk when they think they have someone who deserves to know. You can make them know you deserve to know more about them.