Start your essay by saying that you got this wish granted that you could be superman for a day. Narrate about how you immediately felt and then what exactly are your super powers. And then narrate what you did , how you excited your friends. And then narrate about an incident where you as superman portray as the savior of the situation. Now-by the end of the day, you return to your normal life and you could conclude your essay by saying that you were day-dreaming of all this that you narrated about.