Don't write run-on sentences, they are hard to read. Tell me what you know. Employ the vernacular. Even if a mixed metaphor sings, it should be derailed. Everyone should be careful to use a singular pronoun with singular nouns in their writing.
Exaggeration is a billion times worse than understatement.
Foreign words and phrases are not apropos. Go around the barn at high noon to avoid colloquialisms. If any word is improper at the end of a sentence, a linking verb is. If you reread your work, you can find on rereading that a great deal of repetition can be avoided by rereading and editing. Its important to use your apostrophe's correctly.