Developing characters

One of the major factors that distinguish a well-written novel from a badly written novel is characterization. I have come across a number of books which fall flat on their faces inspite of having a promising plot, just because the characters were somehow not 'real enough'. Of course there are also cases when just the opposite thing happens; but this is the kind of bad writing that I have encountered most frequently.
So, what makes a character 'real enough'? Before answering let's make the question more specific and narrow in scope. Characters are usually classified as flat and round. Flat characters are those which can be quite easily labeled as 'good guys' or 'bad guys'. They are black-and-white characters. They are mostly found in fairy tales and other plot-driven narratives(think of the characters in 'Dracula' or in the Sherelock Holmes stories). Round characters, on the other hand, are not usually black-and-white but are various shades of gray. Some of their deeds are good, some are bad. They cannot be easily classified as good guys or bad guys. And most of the times(but not always) , the author takes us inside their heads, shows us how they think, to make us understand better why they do the things they do. What is usually called 'literature' is full of round characters. An alternative example is the character of Jason Bourne in the novels by Robert Ludlum. And of course, there are times when you are not sure whether you should call a character flat or round, because it seems to be a little of both.
In this post, we shall focus on flat characters. I plan to write another post concerning round characters later. The 2 essential qualities that go on to make a well-shaped flat character are, in my opinion, consistency and idiosyncracy. In fact what I'm going to write is also true for round characters, but there are a couple of extra qualities that need to be considered for them.
Plainly speaking, consistency means that your character always conforms to the attributes that it is supposed to have. That is to say, if your character is supposed to be a 70 year old frenchman, then he shouldn't speak or behave like a college sophomore. Sounds simple? Well, it is NOT. When you are writing a story, then the compulsion for putting in a witty remark or an interesting situation sometimes makes you blind to the fact that you are violating the consistency of your character; especially when you are a novice.Remeber, even if your characters are flat, they have a social,cultural and thus psychological context associated with them. So every time they are to respond to a situation it must be completely consistent with that context. The worst cases I have encountered are when the characters in a story are supposed to be from different backgrounds and still talk like they are twins.
Which brings us to our second point : idiosyncracy. A story becomes that much duller if you cannot tell Mr X from Mr Y. Take for example some Hercule Poirot or Miss Marple novel by Agatha Christie(I didn't say short stoies, because her short stories are short enough to be bearable). Usually there is a murder, and she fills the novel with a horde of flat characters to make the reader confused about the identity of the murderer. The problem is, most of her characters are nothing but a name and probably some physical appearance described somewhere. And it is not as if these characters play a 2-line role either. They are present throughout the novel. So in such cases, I usually had to flip back through the novel, trying to find out who exactly is Mr X and what is his relation to everybody else,everytime he made an appearance. Such characters are the ones that I say are not 'real enough'.As stated earlier, every character has a context associated with it. Now,all you have to make sure is that at least the characters that keep appearing throughout the novel have distict contexts and thus distinct personalities. Your character must make a distinct impression on the reader when he appears the first time, and that impression should be maintained, or should undergo a logical change whenever it reappears. In contrast, consider Dracula. There are many minor flat characters in Dracula that appear only once or twice, but they make a distict impression. In fact, there is one character that doesn't even make a direct appearance, but still leaves an impression. I still remember professor Van Helsing recounting his conversation with a seaman, saying, "He said many things with blood and bloom". What Bram Stoker has done here is quite brilliant. He is reinforcing the idiosyncracies of the Professor's character (civilized, old frenchman) by making him say this instead of something like, "He cussed a lot", and he is lending a distinct character to the seaman under discussion by pointing out his habit of saying 'bloody' and 'blooming' in almost every sentence.
So, to summarize, I would say that a well-shaped flat character must have a distinct personality, and his speech and actions throughout the story should be consistent with it. I will elaborate these points further, and discuss some more complex issues when I write the post about round characters.