Travis asks: I find that whenever I try to write dialogue, I have a lot of trouble really giving it a sense of life. Do you have any advice on how to write dialogue that doesn't just feel flat?
I don't know if I'm the best person to answer this, but I'll take a crack at it.
Dialogue needs to accomplish one or more of the following (not in any order of importance):
1. It needs to help define the character speaking the dialogue.
2. It needs to help define the relationship between the two characters interacting.
3. It needs to provide exposition that informs the reader in a manner that should feel natural and unobtrusive while providing the reader with details that help them understand the story.
4. It needs to help move the story forward.
In terms of comic books (and movies) much of the above can, and should, also be accomplished visually rather than through dialogue.
My best advice really is:
1. Really understand who your characters are. This makes the job much easier overall, because this understanding informs how they will act, or react, in certain situations, and how they'll interact with a wide range of other characters. It will also make it much easier for you to figure out how they'll talk.
2. Figure out what needs to be accomplished in each scene. How much of this can be done through action and how much of this needs to be covered in dialogue.
3. What are you trying to accomplish with the dialogue? Is someone merely giving information? Are you trying to demonstrate that the two characters have a history and are either comfortable with each other or uncomfortable?
The page above taken from Midnight, Mass. #4 (with art by Jesus Saiz, Jimmy Palmiotti and Kevin Somers and lettering by John Costanza) is just this sort of use of dialogue. The story itself is not really moved along by it, and the amount of key information that serves the plot is minor, but it establishes Harmon (with the beard) as a really unlikable person, but yet someone with enough clout that Adam and Julia, the wealthy stars of the story, will still come and work for him even though they can't stand him.
4. Relax. Don't try too hard. Real conversation is peppered with awkward phrases, misused words and tangents that go off subject. While I don't recommend using "um" as a comma, or "like" as it's used in common speech, using asides is okay. Because so much of my work is fantastical in nature, I try to ground the fantasy in reality by balancing the fantastic with the mundane in the conversations occurring on the page.
In the scene above from the never published Xombi Hanukkah Special (with art by Guy Davis and Noelle Giddings) the dialogue contains exposition about the people they are on their way to see but never reach (which happen to be Adam and Julia Kadmon from Midnight, Mass. ) with some mundane asides such as directions and comments about the weather and road conditions which while seemingly inconsequential make the conversation feel more natural and more real while at the same time signaling the danger to come.
The two examples above go about contrasting the fantastic and the mundane in a different way. Both pages add interesting visual contrasts to keep the exposition in the dialogue from feeling boring or chatty. In the top example from Midnight, Mass. #1 (with art by Jesus Saiz, Jimmy Palmiotti and Hoelle Giddings and lettering by Ken Bruzenak) the purpose was to humorously contrast with boring business, which grounds the fantastic in the real world, with the weird activity in the background.
In the second example from Midnight, Mass. - Here There Be Monsters #2 (with art by Paul Lee and Sherilyn Van Valkenburgh and lettering by Janice Chiang) a lot of things are happening at once. An extract from a longer scene, the main action features the Kadmons dealing with a haunted severed hand and the malignant spirit inhabiting it. The main purpose is to lend visual interest to a scene in which a lot of exposition and speculation is given about a separate case which is the focus of the story as a whole. By having the characters discussing something that doesn't have anything to do with the action at hand, I'm also showing that dealing with supernatural threats is just a job to them, just as guys roofing will talk about something unrelated to what they are actually doing when they lay down a roof. The dialogue also contains material that illuminates the relationship that Adam has with his grandmother and gives hints about the mysterious nature of his absent grandfather.
The key is to tell only what you absolutely need to to keep the reader from feeling lost and to allow them to move forward with the story, but also to tell enough so that they can fill in the missing blanks on their own, or feel like they are filling in the blanks so that they become caught up in the story enough to want to stay with it to find out if they are right.
As long as you have that bare minimum of essential information present, you can start building your characters and the world they inhabit through the way they speak, make asides, joke, criticize, and so forth when they are exchanging this information, and will make it seem more like real people talking. This also gives you room to breathe and to allow the conversations to play out in a less forced manner, and you may discover something about what you're writing that surprises you and your readers, and adds to the quality of your story.
For myself, I find that by not planning out more than just the barest bones, I can let the characters respond to one another as well as the situations they are in in a spontaneous manner that seems to be coming more from them and less from me which also makes what they say feel more natural. When you do it this way you'll know you're doing it right when you want to have one of your characters say something and realize that they never would say what you need them to.
Remember also that fictional characters don't really talk with one another like real people do. It's more of a stylized representation meant to approximate and suggest how real people sound when they talk with one another. Depending on the medium, the abstraction of this stylization is more or less apparent. Plays are probably the least like real speech. Comics, because the dialogue is as much a visual element as the images, are abbreviated approximations of real speech otherwise the pictures would be completely covered with dense word balloons.
The two exercises which may help you are to go sit down in a Starbucks and eavesdrop in on a conversation happening at the table behind you. While you're listening, write down what you hear, and then later reread this as if it were a scene. What's being told in that conversation? What is essential to the scene? What's not essential, but helps define the people who are talking? What should be cut from this conversation? The other exercise is to take a pair of your characters and simply write a back and forth exchange of dialogue between them. The conversation should have absolutely nothing to do with your story. They can talk politics, discuss a book they both read, or a meal they've eaten, or gossip about someone they know. This will give you a better handle on them as characters and on how they talk and should help improve how you write dialogue.
I don't know how much of this will really help you, or anyone, and I'm not sure how useful those examples are that I've provided. It's really just some thoughts I have on the process based on your question. Feel free to ask me more if you want me to elaborate, or add something I left out.