Dialogue can arguably be one of the most, if not the most, important part of characterization. And it’s not about what the character says, but how he says it. While the formatting of the dialogue in a screenplay or comic book is different than from a novel (and for you novel and short story writers, I have something extra for you about dialogue), the character still needs to sound real, and his personality needs to show in the words he uses and how those words are arranged. “I challenge you!” is a completely different personality than “Come at me, bro!” and can also be used as a means to show the overall culture the character has grown up in. Another thing to remember is that people who know each other are not going to say each other’s name at the end of every other sentence:
“Did you take a look at this, Bart?”
“No, Bob, I didn’t.”
“What do you think of it, Bart?”
“I think you need to stop saying my damn name all the time, Bob.”
“Look who’s talking, Bart.”
Unless they’re having hot steamy sex with each other, and even then it’s done passionately:
“Yes, John, yes!”
“Oh, Betty, oh—wait! My name isn’t John!”
Also, wasting precious time (and pages) on idle chitchat that does nothing to progress the story along or helps reveal character depth is, well, a waist. Cut it out, preferably with scissors dabbed in gasoline and set on fire. And for God’s sake, stop having humans talk like robots! Robots talk like robots! Humans talk like humans—except when it’s Mitt the Rombot, but he could be a Cylon, so….
Now that you have a good idea of what not to do, I’ll leave you with a tip on a “to do” that often gets missed: body language. Over 75% of communication is body language, more than the words out of your mouth, more than even how you say those words, your body language is what gets picked up on the most. The characters in your story should be no different. Even the makers of video games understand how important body language can be. With movies and plays, it’s the actors who get that responsibility. With graphic novels, it’s usually the artist with some minor input from the writer on occasion (unless both writer and artist is the same person). But for novels and short stories, well, it’s all you, baby. So stop forgetting about body language.
Now go start crafting some good dialogue!