One should never generalize. Tell me what you know. 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. This document is also available in Ebonics.