Different thinkers would have different standards, just as different religions do not agree on biblical interpretation, signs of God's pleasure or displeasure, and on what constitutes good and evil. Some religions stress faith; others, works.
Rationalists either start from the bottom and work up or from the top, down. If they start from the bottom up and reason through empirical evidence and science, they work up to pragmatic conclusions about what seems to work best in the universe, be that guarding the environment, taking care of poor and sick people, working for the good of one's own community, dealing honestly with others and setting a standard for them to follow, etc., until they have devised for themselves a set of principles (or even a first principle) that seem to be the best ones to live by for the good of the earth and of its peoples.
Or you can start from the top and begin with one principle from which you derive all others. One example of this might be Kant's categorical imperative: For Kant, there is only one imperative that commands us unconditionally and this is the Moral Law: "Act only on that maxim whereby thou canst at the same time will that it should become a universal law." (More on this:
http://photography.cicada.com/sp/kant.html) If you set this as the guiding principle of your life, all opinions and actions would have to flow from it and not contradict it.
If one's mind is not up to the task of creating a world view, there are many thinkers, past and present, who can be consulted for help in establishing one's guiding principles. I would include Jesus Christ among those thinkers. He was a great spiritual leader and thought outside the box. A thinker can consult Christ's thoughts and principles even if the thinker doesn't believe he was "the son of god."
Without the "authority" of god, or the fear of having an unhappy afterlife, one's principles are enforced from within. The reproach of one's conscience can be as terrifying as the thought of hellfire.