Characters
Types of "good" characters
Good stories have good characters, but different people will define "good character" in different ways. Some possibilities are a character that is likable, that the reader is able to empathize with, that is complex and interesting.
Interesting, I think, is one of the keys. Some people will only read a character they like (Samwise Gamgee, for example, is a likeable sort); others think a character is good even if s/he is not particularly likeable at all, but is still a complex and interesting such as Hannibal Lecter. Figure out what you're aiming for and focus on that.
It's generally important for the reader to understand the character and why they do what they do. Enigmatic characters can be interesting, but rarely (if ever) do they succeed as a Point-of-View character--without understanding/empathy/connection the reader feels like s/he is reading a collection of seemingly random events, and feels no attachment to the story.
Making Unique Characters
A character is not made unique by his or her powers, lineage, or physical description (at least not physical description alone). A character is distinguished by personality and action. Readers want characters that think and act; through these thoughts and actions a character is created.
What this means in practice is that writing out your characters statistics and life story doesn't mean you have a good character. A good writer can, in one sentence, create a better character than a bad writer with 100 pages of background material. You begin to truly create a character once you have that character reacting to things, making decisions, taking action, etc. In general, have your character do things. Have there be a reason--a reason based in the personality you want to project--for why that character is doing that, or saying that, or thinking it, or whatever.
Sometimes this process is as simple as giving the reader something about the character that interests them, be it some bit of dialogue or a physical description, and then proceeding to make the character complex through thought and action.
Flat vs. Complex/Developed Characters
A well-written flat character is one that acts consistently in the role s/he is meant to play. So you might have a witness that the detectives need to interrogate. It's a likable guy who answers some questions, gives the detectives a vital clue about his old roommate, and then is never heard from again. He isn't badly written; he serves his purpose, and thus requires no complexity. If we need him later, we can develop him into a more complex character then.
A complex character should able to contain contradictions and extremes. The better you establish the solidity of a character through good writing, interesting action, dialogue, etc. the more that character will be able to do and still feel like s/he hasn't done something out of character. It helps if this is backed up by what I'll call dramatic logic. In moments of high tension and stress--basically moments of high drama--people are much more likely to act in ways they normally wouldn't. You can use this principle to have your characters act in ways the reader might not predict, so long as they have a feel for the character. Essentially, once the reader has a feel for a character's boundaries, these boundaries can be stretched.
The final piece to the complex character puzzle is character change. People like characters to change in stories. Complex characters _should_ change--we all change over time, and everything we do affects us somehow. How do you change a character? By stretching their boundaries! Whee!
3nodding
Written by Carrot Ironfoundersson
Dialogue
So, you want to write interesting, realistic dialogue, and you want it to convey personality and plot information at the same time.
There are a few things to remember. Dialogue can be one of the most important parts of your story. It's said that children look for pictures, adults for dialogue. When a reader is getting bored with your description, they may just look for the next bit of dialogue. What does this mean? Well, it means that you should try to make every part of your story engaging, and of course dialogue is a part of that.
One thing to avoid is back-and-forth dialogue. Sure, it might be how people talk, but it's not very interesting to read. It's very low tension, it often doesn't allow the personality of your characters to come through, and it can come off like you're just trying to dump information.
What I mean by back-and-forth is dialogue where people ask and answer each other's questions in a very linear way, often with a lot of yes or no questions. "Hey, did you hear what happened the other day?" "No, what?" "I almost got hit by a car!" "Oh my gosh, really? Are you okay?" "Yeah, it was speeding around the corner when I was about to cross." Etc. Answering each other's questions, responding directly to only things that are said (as opposed to all of the things we leave unsaid in our conversations every day-- think about it!).
Related Links
BabyCenter-- Find names by sex, ethnic origin, number of syllables, etc.
Behind the Name- the etymology and history of first names