NEVER, NEVER ...
Begin a sentence with a pronoun.
Begin a paragraph with a pronoun.
Use ambiguous pronouns: this, that, those, it, etc.
Write like you speak. That is, do not use a conversational style that screams out: “I am not serious.”
Use words you do not understand. If you misuse a word, you will lose credibility.
Use more words than you need to use to make your point.