Write an essay in the standard format The introduction contains your thesis statement (what the essay is about or what position you are taking). Follow with the body of the essay and end with a conclusion that answers the issue your thesis raises.
Strip out any references to the first person, such as "I," "we," and "us." Replace them with third person counterparts like "he," "she" and "they" or, more commonly, erase them completely. "I think schools should have stricter dress codes" could be condensed to "Schools should have stricter dress codes."
Remove references to the second person--"you" or "your"--as well Note that first- and second-person references inside of quotes ("'We are met on a great battlefield," Lincoln said.) are fine.
Scan your document for related grammatical errors: make sure it is consistently in one tense (usually past or present) and look for typos or spelling errors. If possible, ask someone else to read it over as well.
Make sure to cite all of your sources according to the rules laid out by your teacher or boss.