First, I would try to do right with my power. Become a paragon of virtue and change things for the better. Then, frustrated with a lack of progress and change, I'd go full tyrant on planet Earth until I realize that you can't force utopia on people, either. Then I'd relent, relinquish the sovereignty of this world to the annoying little protozoa that think themselves rulers of this planet and watch the self-proclaimed "people" of the world destroy themselves and their environment, not necessarily in that order, wondering all the while if humanity is worth saving when humanity is the biggest enemy to itself.