Intelligence is a skill, and like any other skill you need to be interested in it and practice it. find some topic that interests you; read about it, think about it, and talk
… about it until you feel you understand it. then when you feel you understand it, find someone who disagrees with you and try to understand why they disagree. don't worry if you feel a bit stupid - intelligent people often feel a bit stupid, particularly when they're just starting to learn something (most people are unaware of how much they misunderstand the world, which allows them a very unjustified self-confidence). (MORE)