Parenthetical remarks (however relevant) are unnecessary.
It is wrong to ever split an infinitive.
Contractions aren't necessary.
Foreign words and phrases are not apropos.
One should never ever generalize.
Eliminate quotations. As Ralph Waldo Emerson once said, "I hate quotations."
Comparisons are as bad as cliches.
Don't be redundant; people find constant repetitiveness a turnoff. Repeating things already said can be annoying to others, as well. Besides, it makes people mad.
Be more or less specific.
Understatement is always best.
One-word sentences? Eliminate.
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.
Who needs rhetorical questions?
Exaggeration is a billion times worse than understatement.
Don't use considerably more words than those which figuring one way or another are really necessary.