Writing good dialogue is hard.In comics, that is the writing flaw which shows up the fastest. If you know nothing about character development or plotting, those will take a few scenes to surface. Dialogue, however, can sink you in a single panel. I think that I am pretty good at doing dialogue... though I do fall into the same traps again and again. But this is true of even the best writers. Every person has only one view of the world, despite how well they may take on other views. In some way or another, all of my writing is going to sound like me. But, to work as hard as I can to avoid repeating myself, I have gleaned a few tactics from the reading and experimenting I have done. Here's a bit of it. These are some guidelines I follow when I am writing dialogue. This is just my approach, there are many others that work very well for lots of pother people. Usually I start by vomiting out huge passages of rambling, repetitive, chatter that generally gets out what is going to be said. Then I run it through these filters.
1. Show character. This is not just words on a page. this is a person opening their mouth and letting others know their thoughts. This means something. Basically, I ask "how would THIS person say this?" Is she shy? Academic? Bold? Stupid? How can those qualities surface in word choice? In speech pattern? This is the first level, where it starts to look like that person in general. If it isn't quite coming through, I have another trick or two. 1a. Base it on people you know. Or, failing that, actors. When it comes to how they talk, I base almost all of my characters on people I know. Or if I can't think of someone I know, I think of an actor I know of who could pull it off. Once I have that character model in mind, I take the raw dialogue I wrote above and strain it through this person's mouth. How does it sound with him, or her, saying it? This will change a lot of the word choices and cadences. With flat. stock, or background characters, this is often enough. 1b. Don't show off. This is more a warning against bad dialogue than a rule for good. Don't try to sound like a scientist or a cop or whatever. Sound like a person, and then add some cop words on top of that. Don't try to write great dialogue. Write natural dialogue in great scenes and it will seem great.
2. Show background. Realistically, you can't use this one every time. There are some situations where an individual's background simply does not surface in their speech. However, if you dig you will get more mileage out of this filter than you think. Essentially, you ask yourself how this character's unique background would affect what they are saying. At the shallowest level, this is accents and regionalisms. What does he talk like? Deeper than that, look at the position life has given your character. Someone who has worked in restaurants their whole life is going to ask for help in a different way than someone who has only even been waited on. Someone who is ashamed of their ignorance is going to speak differently than someone who is fundamentally curious. This is not a mandate "You MUST show background", but rather an opportunity "how can this background come through in what is being said right now?".
3. Show perspective. Ok, this one is more like a mandate. Especially when page space is limited. If you are not showing some unique perspective, then shut your mouth and let someone else talk. Perspective is related to background, but it is more specific. Background never changes. It is who you are. Perspective, on the other hand, changes from moment to moment. It is how the world looks to you right now. When you are relaxed and comfortable, you have a very different perspective from when you are terrified. When this guy says this thing at this moment, what does it mean to him? "What do you want for dinner?" can mean just that, but it can also mean "I Still love you and your well being is important to me." That depends on the character's perspective at that moment. For this filter to work you have to really get inside your character's head. This is where great misunderstandings and unanswered questions can come from. A character who is feeling shaken from a previous interaction may take a simple question as a flagrant challenge to his authority. Or a character who is giddy on the high of a new relationship may completely gloss over relevant details. This is similar to showing motivation. Every writer has a slightly different approach to finding this level. Again, not every line of dialogue is going to reveal this level of depth. But if it isn't, that is a good red flag. If you are not showing perspective, do you need this line?
4. Less is more. This is a tough one for me. I like my dialogue. I like the way my characters talk. A tend to want them to just talk and talk. But space is limited, and a little goes a long way. People in comics do not talk like people in real life. Don't try to make them. One stammer in an acre of word balloons is enough to let the reader know that this person is insecure right now. One dropped 'r' is enough to show a Boston accent. Let it go. Trust your reader.
And to demonstrate that less really is more...