William Safire's Great Rules of Writing

Do not put statements in the negative form.
And don't start sentences with a conjunction.
If you reread your work, you will find on rereading that a great deal of repetition can be avoided by rereading and editing.
Never use a long word when a diminutive one will do.
Unqualified superlatives are the worst of all.
De-accession euphemisms.
If any word is improper at the end of a sentence, a linking verb is.
Avoid trendy locutions that sound flaky.
Last, but not least, avoid cliches like the plague.