Marcus Aurelius wrote:
Concentrate every minute...on doing what is in front of you with precise and genuine seriousness, tenderly, willingly, with justice. And on freeing yourself from all other distractions. Yes you can - if you do everything as if it was the last thing you were doing in your life, and stop being aimless, stop being hypocritical, self-centered, irritable. You see how few things you have to do to live a satisfying and reverent life?
Meditations 2.5
After reading Meditations , this particular one seems to sum up so much of the book. Life is not permanent, so act accordingly. And you have control over how you act and react. These ideas cover almost everything.