Understatement is always best. Analogies in writing are like feathers on a snake. 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. Do not put statements in the negative form. 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.