Let's think about this logically. Writing fiction is about telling a story. Every story revolves around a plot. Every plot is carried out by characters, and characters carry out the plot through action and dialogue.

Dialogue comes from characters for the purpose of advancing plot to tell a story. Therefore, dialogue should only exist to serve the purpose of advancing plot and revealing character motivation or history that in turn advances the plot. That's why dialogue exists.

This brings me to my main point. If you take away nothing else from this article, take away this: Only write dialogue that serves the purpose of advancing your plot. If it doesn't, cut it out of your story without hesitation or remorse.

Secondly, conversations in stories should not be anything like conversations in real life. Real life almost never has a plot, and talking almost never reveals motivation or history because there's no plot to life. Therefore, if you're trying to make your dialogue as "true to life as possible," you are inherently failing to tell a dramatic story.

Stories are distinctly different from real life. If real life were the same as reading or watching a good story, no one would endure the effort, time, and possible insanity to create them. We create stories because we want a break from what's real. We want to enjoy something larger than life. We want to experience something that makes sense, that we can connect with, and that makes us feel.

I realize none of that will actually help you write better dialogue. Here are some tips that will.

- Always be in charge of the conversation. Contrary to popular belief, your characters can't talk on their own. Sure, they have their own voices, but they exist inside your head. Yes, you are the one making them speak. It's ridiculous to think that you don't have control over what your characters say and do. You absolutely do, and you can step in and redirect them, cut them off, and change their worlds whenever you want. If you're not doing that, you're not in charge of your story, and it's not going to turn out very well.

- Like in ever other aspect of storytelling, enter as late in the conversation as possible and exit as early as possible.

- Remember that every character has an agenda. Everyone wants something out of every conversation. If they don't, why are they talking? The shouldn't be, so shut them up.

- Be as concise as possible. Maybe people in real life talk too much and say unnecessary things. Fiction is called fiction because it is distinctly not real life, and there should never be any unnecessary words anywhere in your story.

- For the love of all that is holy, don't use clichés. If you find your characters using them, stop and take the time to word whatever they're saying differently. And more interestingly.

- Be unexpected. One of the worst things you can possibly do when writing a conversation is to write dialogue your audience will see coming. Again, people seek out stories because they want an escape from reality. If they know what's coming, you're failing to do your job. If you're dialogue begins to feel mainstream, stop, think about how you can make it more interesting and less predictable, and try again. You can do it. Writing should never be easy; if it is, you're doing it wrong.

- Be logical. Always know why your characters are saying what they're saying. They might make sense to you but not to someone else, so always pay attention when anyone points out something that doesn't make sense to them. Chances are, it's not because they're stupid and don't get your story. It's because you haven't done your job well enough. So revisit it and rework it until it does make sense.

Lastly, here's a list (certainly not all-inclusive) of things you should have planned out or at least generally know in your head before you start writing a fictional conversation:

1) What led to this conversation
2) Why this conversation is important to the plot
3) What each character is trying to get out of the conversation
4) If they will actually get what they want out of the conversation
5) What drama and tension this conversation will create (If it's not creating any drama or tension, you're wasting your time.)
6) What will change from the beginning of the conversation to the end (If there's no change, again, you're wasting your time.)
7) How each of your characters will respond to the other(s)
8) What character actions and/or reactions this conversation will lead to
9) How you want your audience to perceive this conversation (Is there subtext? How about foreshadowing?) and how you want them to react emotionally (You know you did something wrong if they don't react the way you expect.)
10) What happens next as a result of this conversation (Didn't I say story consists of characters carrying out plot through dialogue and action?)

Maybe this wasn't what you were expecting, but I've had a crap-load of experience writing, reading, and watching dialogue both good and bad, and this is what I've learned. If you have any experience with good fiction, you've seen that all good dialogue follows these guidelines. I didn't make them up; I merely observed them, and I hope my observations will help you create more compelling fiction.