Love God with all your heart mind and soul, and,
Love others as you love yourself.
Then the Holy Spirit lets you know when you are doing wrong, you don't need a Chrsitian to tell when you are doing wrong or right.
Then God will judge you when you die, and probably just the way you judged others and then some. But I believe its relative to the person, not a set of rules. I hope he judges us based on what we know. If we don't know God, then how can we love him?