Do you say yes to the demon?
A demon comes to you at the end of your life and asks whether you would live your same life over and over again for eternity. Nietzsche says that if you are living well, you will say yes. I say this would be boring.
Instead, if the demon asked whether I would live my life over and over again for eternity using the same decision making process as I do in this life, then I would repeat my life eternally with joy.
What are the decision making criteria that lead to that conclusion? The answer to that question is how to live a good life.