I had this story draft, and it was missing something. (If you have written for any length of time, this may sound like a familiar scenario.)
I figured it out eventually: it was being too well-behaved. Following to the outline, characters doing what they were supposed to do - for perfectly good reasons, mind you, but they were awfully obedient. Too obedient.
They needed personality.
Of course, this will surprise no one. Certainly characters need personality! But what I needed from my characters - what was missing - was not so much backstory and general motives but a sense of each one as a force in the story.
This is what I mean. A character who is a force in the story will be a force for good, or evil, or for chaos, or a force for goofiness, or something like that. When that character walks into a room, you immediately say, "Okay, now things are going to get _____" (Fill in the blank with good, evil, chaotic, goofy.)
I picked the following quote up from Jamie Todd Rubin's website where he recently reviewed a book by George R. R. Martin:
"Another remarkable aspect of A Clash of Kings–for me at least–is that the characters are by now so well developed that as a reader, I felt like I knew them and could guess their reactions to various events."
This is something like what I mean. Because you know what kind of person they are, and what they'll do in a certain situation, they have more dimension. This can be big stuff, like mental illness (for my character Nekantor who is a force for order, and not in a good way) or heavy backstory. It can also be little stuff, like some detail of their self-image that affects their interactions.
I'll give you the example of the characters I've been working with: Adrian Preston and his wife, Qing Preston. Both are linguists. Both are accustomed to working with aliens and taking them seriously. So far so good. But they weren't different enough, and they weren't forces. So I decided to go further with Qing's Chinese background and give her a Chinese nickname for her husband. I looked around on the internet and came up with Big Bear (this is of course the translation). Then I suddenly realized that Adrian should be a genuinely big guy - and self-conscious about it. But then I decided he couldn't be so self-conscious that he was timid. More playful. And from there I got to the fact that each one of them loves being a linguist, but for different reasons. For him, language and culture are all fun, never work, and he just can't get enough. For her, language and culture are such serious business that she devotes herself entirely. Suddenly I saw both how they would be able to work toward the same goal and how they would encounter conflict along the way. They would be able to do what I needed, but they would have personality, and each one would have a different form of influence on the story.
All of a sudden I really want to go write this thing.
It's something to think about if you ever feel your characters aren't quite coming to life.