Less Wrong's about page notes that it is "devoted to refining the art of human rationality - the art of thinking." Rationality is given a more thorough introduction in the post What Do We Mean By "Rationality"?. Also of help are the Twelve Virtues of Rationality.
Believing, and updating on evidence, so as to systematically improve the correspondence between your map and the territory. The art of obtaining beliefs that correspond to reality as closely as possible. This correspondence is commonly termed "truth" or "accuracy", and we're happy to call it that.
Achieving your values. Not necessarily "your values" in the sense of being selfish values or unshared values: "your values" means anything you care about. The art of choosing actions that steer the future toward outcomes ranked higher in your preferences. On LW we sometimes refer to this as "winning".