Principles
Rationality, or the life of the mind, is not enough to live the good life. One must set one's house in order. One must control one’s impulses in terms of eating, and one must exercise one's body. One must live the golden rule and lift others, seeking to alleviate their suffering, and one must seek out beauty to nourish the soul or die spiritually.
Hopefully these principles help build habits that allow one to live a life of virtue, Aristotle's view of virtue: structuring one's life so that one's instinctive responses line up with one's reflective commitments. That is the good life. That is all that one can ask for.
How Should I Live?
In addition to the above answers, the question "How should I live?" is tantamount to asking "How should I spend my time?" No one can answer that question for everyone, but this Brain collects some attempts to answer that question for myself. See also Time Management & Organizational Skills and Purpose Greater Than Self ("Calling?")