The passive voice is to be avoided. Go around the barn at high noon to avoid colloquialisms. Even if a mixed metaphor sings, it should be derailed. Exaggeration is a billion times worse than understatement. Don't never use a double negation.
Verbs have to agree with their subjects.
Proofread carefully to see if you words out. If you reread your work, you can find on rereading a great deal of repetition can be avoided by rereading and editing. A writer must not shift your point of view. And don't start a sentence with a conjunction. Place pronouns as close as possible, especially in long sentences as of 10 or more words, to their antecedents.