Forgive my pontifications, but one thing which ultimately hits a strong but subtle wrong note in stories and theatre is bad dialogue. By this (for now) I mean the lack of a genuine voice for characters.
As a playwright, I frankly regard dialogue as the single biggest aid for me to give the director and cast. Partially this comes from my study of Shakespeare, whose plays literally brim with clues and hints about how to perform them. One of the most obvious is when he either add or omits a beat from the ten beats of a typical iambic pentameter line. He always has a reason that for that. Always. Usually indicative of an extra stress somewhere, or sometimes a break in the rhythm for effect (Hamlet--the character--has a fair amount of this). Another lies in the way a regular ten-beat line is often divided between two (or more) characters--which means essentially don't take any pauses here.
But all that lies in verse. One can find countless examples in prose as well. Alas, too often you don't find them. So I'm going to pontificate and offer a guide, a series of hints to help fellow writers develop or hone their skills in this direction. Mostly a matter of questions to ask.
First, when does your character interrupt someone else? If they do such easily and often, clearly this makes them a fundamentally different person than someone who never or rarely does at all. But of course it must be more complex than that, yes? Yes! For one thing, you have more than two options--Often versus Never represents two poles, with an infinite variety in between. This in turn leads to specifics. Who will your character most likely interrupt, and why? More, under what circumstances? Even more importantly, how do they interrupt? A polite raising of the hand coupled with the words "Excuse me, don't mean to be rude at all, but I feel something needs saying..." shows a very different personality than the sudden bark of "Wrong, wrong, wrong! You've forgotten something!" Likewise, a quick point of finger with an intense but unemotional "Question--if that were true, what prevents...?" displays a different one from a sudden rising out of the chair, eyes blazing and words spat between clenched teeth "How...DARE...you!" All different, albeit only a few of the many possibilities. All belonging in your writer's toolbox. Kindly remember while you're at it--characters will interrupt in different ways under different circumstances. The most well-rounded of such might use every single one of the previous examples. Every single one. But--why?
Possibilities abound! A teacher, for example, might interrupt the Dean in one way, their students in another, a sibling in still a third, their spouse in a fourth, their own children in another, and so on. Ditto a student, a priest, a carpenter, etc. This is hardly about choosing one option for a character, but understanding which options they tend to use and when.
Second, consider how good is your character's grammar? Honestly, George Bernard Shaw sometimes takes this idea to almost ridiculous lengths. In Major Barbara for example he writes out lower class London speech phonetically, and while somewhat helpful this also can generate headaches. Yet in truth the basic idea holds. A person who says "Where are you headed now?" seems not of a different class but of a different personality than someone who says "Where you going to?" It might or might not indicate amount of education, but assuming someone in our culture and era, this person's attitude to speech and language comes through. Not a matter of carelessness, either. More a taste in terms of what is technically correct or maybe proper. After all, don't you perfectly understand both examples? A fairly easy pattern to note, yet not quite obvious, lies in the use of double negatives. Again, a matter of degree rather than either/or. "I don't have any pastries" certainly sounds alien in the mouth of someone who more usually will utter "I don't have no cakes today" just as will the equally ungrammatical "Now I don't have none cakes, I done told you." But this offers yet another area of nuance. What makes someone who uses (for lack of a better word) sloppy grammar start using absolutely correct grammar? Or at least try to (and perhaps fail)? Likewise consider the circumstances that might lead a person to start using double negatives or other grammatical errors (ending sentences with a preposition, for example). Then again, think about those obscure forms of speech which, while correct, rarely end up used in day to day speech. If I were to go there (as opposed to if I was) or perhaps To what school is Henry going? (rather than What school is Henry going to?).
Perhaps most interesting is how all these reflect not only character background, but even more importantly character attitude. Consider John Smith. A more generic proper name in English seems hard to imagine. Give him something to say. Anything. Preferably at least a sentence or two. Now, listen to John Smith say those lines in your head--but with variations. Suppose he says those lines as an interrogator--maybe a private detective, an attorney confronting a witness, a husband suspecting a spouse of adultery, etc. Or suppose he says them as a supplicant--speaking to a ill-tempered manager, a teacher upon whom he has a crush and feels hugely intimidated, a police officer when he knows there's an unpaid parking ticket from last year in his wallet, or so forth? Perhaps he speaks as a salesman, as a professor, as a spy, as a would-be suitor? The line changes does it not? In fact, you'll probably find yourself wanting to re-write the lines.
Did you notice what I did there? I changed John Smith's role. This needn't indicate he has any one of these professions (although he might). Rather it notes what mode he's in at the moment, identifies the context of his lines. That context will always and forever remain vital--the history, the place, the time, the other characters listening, and where John Smith is at that moment in his own mind. Ashamed? Furious? Exultant? Annoyed? Drowsy? Terrified? Some combination? (Here's a hint--it is nearly always some combination).
Finally here's a list of different speech and conversation patterns from life. Some might never occur to you. Others you'll recognize instantly. Please feel free to add to the list! No doubt you know things I do not, and I'd appreciate if you shared!
- Some folks never ask about others, but regale people with compelling details of what's going on in their own lives.
- Some speak rarely, but when they do their words sound awkward, as they try and find the right wording on the cuff.
- Some immediately ask questions, presuming others can answer in detail about their own plans and hopes and long terms goals as if giving a powerpoint demonstration.
- Some have zero patience with any idiosyncrasy of speech with others, reacting with different degrees of patience while asking what the hell someone else is talking about?
- Some always change the subject, not to themselves per se, but to areas and things that interest them, like pet theories or specific ideologies.
- Some long to explode in rage and pain, but have learned to control themselves, with every tiny bit of politeness a subtle moan of pain.
- Some litter their speech with things like "as it were" or "as far as I can tell" and other clusters of words that may come across as filler (but may have some very practical purpose).
- Some demand precision in their speech, actually working out it has been nineteen and a half years since their sister graduated high school, not twenty.
- Some overuse certain words such as "like" "that" "whatever" "so" "then" etc.
- Some rarely use certain words at all, such as "I" or "need" or "evil."
- Some scatter their conversations with homilies or reworked quotes, sometimes original little bits ("How are you" "Oh fair to partly clowdy")
- Some people argue for the sake of arguing, sometimes to the point of not really paying attention to what they're saying (like the Pro-choice college student who won't even remember claiming parents should have the right to euthanize newborns if they don't like what they've got).
- Some hate it when a subject changes and will steer the conversation back, regardless of whether anyone else wants to return there.
- Some change the subject seemingly with every breath, and show little or no awareness they've done it. Or maybe they know they do it and apologize every single time--while still doing it.
- Some state their opinions as fact, acting baffled and insulted that anyone could disagree.
- Some are so interested in hearing what other people have to say they keep stirring the pot just to get others to reveal more of their ideas.
- Some people vent all the time--when their computer isn't as fast as they want it to be, when a lightbulb goes out, when anything begins early or late--seeing this as healthy, viewing those who don't as possibly hurting themselves.
- Some want peace, longing to avoid conflict save in the most joking manner.
- Some people have real difficulty grasping metaphors or hyperbole, taking things quite literally even when hardly anyone else does.
- Some frankly state certain subjects hold no interest and expect people to then not go there. Sometimes these folks accord the same courtesy to others--once someone states disinterest, they change subjects. Sometimes they don't.