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.
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.
William Safire, Great Rules of Writing
And yet, I'm breaking the rules now. And I do it often. VERY. Often. It just works for me, because conciously breaking certain rules change the feel of what has been written.
I am, however, very finicky about what I perceive to be errors. People breaking rules per accident. It just stands out more and degrades the quality.
So... what's your favorite writing rule to break on purpose?