Do not put statements in the negative form. And don't start sentences with a conjunction. It is incumbent on one to avoid archaisms. 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. Never, ever use repetitive redundancies. Also, avoid awkward or affected alliteration. Last, but not least, avoid cliche's like the plague.