Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

Is there a specific rule, or set of rules, that can be followed to know when to use each word? I have noticed that not is usually used with a verb, but I think that there sometimes are exceptions although I can't think of one now.
Not is a negative adverb; no is a negative quantifier; non- is a negative prefix. Since negation is so important, thousands of idioms use each of these, among other negatives. Consequently there are lots of exceptions to the general rules below. Non- is not a word, but a part of another word, usually a descriptive adjective: non-lethal, non-professional, non-native, non-technical, non-playing (The hyphen is optional.) Each of these mean 'anything but ...' -- anything that doesn't kill you is non-lethal, anything that's not technical is non-technical, etc. This meaning contrasts with un- and in-, which refer to opposites instead of complements. No is half of the answer pair Yes/No, shading off vocally into Nah, Nuh-uh, and Uh-uh. But it can also quantify and negate any noun phrase: Some blade of grass ~ No blade of grass; One who saw it ~ No one who saw it. Not is the general negator for verb phrases, including predicate adjectives and nouns. In a verb phrase, not occurs immediately after the first auxiliary verb. If there is no auxiliary verb in the verb phrase, Do-Support supplies a form of do. Not is contracted whenever possible, with auxiliaries or subjects (especially pronouns): He's not interested ~ He isn't interested; She doesn't like it, but not *She not likes it. Any of these negatives (and many others) can negate a sentence, changing its truth value. It's easy to switch between them, too; the sentences below all mean the same thing: They allowed no phone calls. They didn't allow phone calls. No one allowed phone calls. Phone calls weren't allowed.

I'm trying to find a humorous term for someone who still has an overdue library book after a number of years. I first came up with 'delinquent lendee', but I'm sure there's something more apropos or alliterative.
Here are a few I came up with, choose one that suits you: Book-Bandit Book-Clip Book-Plunderer Book-Pocket Book-Lifter Library-Climber Library-Breaker Book-Breaker Biblio-Bandit Lendup-Artist Biblio-Bezzler Biblio-Prowler Book-Prowler

is it 'a usual' or 'an usual'? 'A usual' sounds more correct in my head ('Today was a usual day.') than 'an usual', but u is a vowel. Which one is correct and why?.

Usual (pronounced /ju.u.l/ as in you) begins with a consonant sound and, as such, it should be preceded by a not an. As an aside, I cannot help but point out that the sentence Today was a usual day is not usually heard in regular conversation. Today was an unusual day is what one might hear, instead! Indeed, I rarely hear the construction a usual. The definite article is more commonly used, in my experience: That's the usual thing. In place of a usual, one would also be more likely to hear not an unusual: Today was a usual day / Today was not an unusual day This is a usual occurrence / This is not an unusal occurrence or This usually happens You are right in saying that a usual sounds weird. As speakers, we tend to avoid constructions which, though correct, do not flow easily from the mouth. In sum, the following are valid and commonly used alternatives: not [an] unusual the usual usually