Depth
Matt G. asked: The burning question for me is character depth. How can you encourage the readers to identify with your characters? How can you add "depth" to characters - so the reader is rooting for them?
This is a fairly difficult question to answer, largely because it's something that took me a long time to get a handle on. I still do it mainly by instinct, which makes it kind of hard to articulate, but I'll give it a shot.
The first point is that "depth" doesn't actually have a lot to do with whether readers identify with or root for a particular character. It's perfectly possible to get readers rooting for characters they don't identify with and who have no depth or complexity to speak of - the popularity of certain cartoons, comic books, and pulp novels proves it. It's perfectly possible for the villain to have enormous complexity and depth…and this often makes for a great story, in spite of the fact that one generally doesn't want one's readers identifying with or rooting for the villain.
My second point is that there's a reason why both Matt and I put scare quotes around "depth" - and that reason is that it's one of those writing terms that gets thrown around a lot, but that doesn't have a terribly good definition. Everybody is supposed to know what it means, and accept that it's highly desirable in fiction. For purposes of this post, I'm going to claim that "depth" in a character means that the particular character has more going on with him/her than just their role in the story - probably a lot more.
All that extra stuff that's going on can come from a lot of different directions. It can be skills or knowledge; aspects of personality; old mental or physical scars; needs and wants; hobbies; relationships. In a novel, some of it may be crucial to one or more subplots involving the character. Some of it may be background experiences that shaped the character. A lot of it may be stuff that's irrelevant to the plot and/or that mostly happens offstage.
The point is that real people have a lot going on. They have jobs and hobbies, relatives and former romantic interests; they dropped out of ballet class in ninth grade but still like to watch (or can't stand going to the ballet because it reminds them); they wanted to be rock stars or firefighters or astronauts when they were nine or thirteen; they get on really well with one sibling but not another (but they'll be right there when either one is in trouble); they have secret fears and crushes. And all of this is part of them, and affects how they act, react, and interact with the people and places around them.
The writer who wants a character with "depth" thus has two things to do: 1) Figure out or make up what all that extra stuff is, and 2) Get enough of it into the story so that the reader is aware that it's there.
The vast majority of "how to do characters" books and web sites that I've looked at assume that the writer is going to do #1 in advance; that is, that the writer can and should start by filling out a character questionnaire that has everything on it from hair and eye color to location and shape of scars to childhood trauma to name of first pet. Which is all very well, if that works for you, but it never has for me. Filling out those questionnaires (some of them are ten pages!) gives me a large, miscellaneous heap of facts and quirks and odds and ends that never manages to gel into an actual character.
I usually find out about my characters during the writing process, as I write. The group sits down to a meal and suddenly there's a fight over who gets the last serving of David's green beans, and suddenly I know that a) David does the cooking, and is good at it, and b) green beans are favorites for both George and Janet, but not Harold (and Sissy likes them but not enough to fight about). And there are writers whose first drafts are really, really thin, who go back during their first rewrite and make the stuff up then. Before, during, or after; it's your choice when to make up/figure out what else is going on with your characters besides the main plot.
And it doesn't all have to be worked out at length and in depth. I may never find out how David became such a good cook…or maybe something more will come out in Chapter 17. In fact, one of the things that provides character depth is that some things aren't ever totally explained; they're just how the character is. What is important is that whatever is in the story is internally consistent - that David doesn't make a gourmet meal in Chapter 3, then is unable to tell the difference between an onion and a head of garlic in Chapter 10.
This is the problem, for me, with the questionnaires. The assumption is that as long as you know up front that Jack secretly knits, hates cats, loves Mozart and the Beatles, and has seen every movie made in English before 1939, you'll remember to use those things in the story when and as the opportunity arises. But if what I have is a big heap o' facts, rather than an idea of a person, I have to keep looking up all the stuff I decided before I can figure out which bit to use (or not use) in a scene. For some people, though, having all that stuff decided up front and written down frees up their imagination to do more important things about the plot and structure when they get to actually writing the story.
As for getting it into the story - you do it the same way you do any other aspect of characterization: by showing it in what the character says, what she does, what he thinks, what other people think and say about them. It all boils down to thinking about what this particular person would do, say, notice, react to in any given situation, rather than just running down the plot checklist.
And you don't have to get all the character's stuff out in the open in the course of the story. Sam's secret teddy-bear collection may never come up during the course of the slam-bang action-adventure he's currently involved in, and that's fine.
Which brings me to a final point: you don't need to know vast amounts of background information about every character in your novel. The doorman at the hotel whose one line in the book is "May I take your bag, sir?" does not need a ten-page background questionnaire. (If you want to do it for fun or practice, fine, but you're not going to need to know all that stuff.) The receptionist that the protagonist flirts with three or four times as she's heading into the office may need a bit more background, but he's not going to need as much as the protagonist herself, nor the protagonist's sidekicks. Trying to develop every character who walks onstage in the same depth and detail will just make you crazy.