Contractions aren't necessary. Foreign words and phrases are not apropos. One should never generalize. Comparisons are as bad as cliches. Be more or less specific.
Understatement is always best.
Exaggeration is a billion times worse than understatement. 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.