Question: I'm 1/4 through my first novel, with a pretty solid 12 page outline of the whole thing. After years of reading books about story structure, I think I have a good grasp on how to make a plot work.

My characters, however, are turning out to be quite flat, uninteresting and generic. They do have motivations and I'm putting a lot of effort into making sure they act accordingly, in a logical way according to their goals and the story seen from their perspective, etc. But they don't feel "alive".

I've read about the archetypes in The Writer's Journey, but that's about it. How can I make my characters come to life?

Answer: 
When I create characters, after creating their appearance and personality, I usually try to think like them. There are almost always some key attributes of a personality, so try being that person for a while. Just thinking like them is enough.

For instance, there was once one truly evil character. For a time I forced evil thoughts to the point when I was becoming evil. I had an evil character, knew how diabolical minds think (to a certain extent) and could appropriately write about him. [:
Making realistic characters starts with knowing them. Pick your top few characters, and write a character bio. To write a bio, you must answer some questions about your characters. Here is a non-exhaustive list of a few questions to answer about your characters:

* Where were they born?
* What kind of family did they grow up in?
* What are their likes and dislikes?
* What do they look like?
* What are their core beliefs? (i.e. moral, religious, etc)
* What do they sound like (voice, dialect, etc)
* How do they interact with others?
* What type of people do they have as friends?
* What type of flaws do they have (everyone has them, and if your characters don't, they won't be believable.)
* What is their back-story?
* What culture did they grow up in?

Each question like this informs your characters, and provides a texture and richness.

Also, your main character should change through the course of the work. The typical method is giving your character a fatal flaw that he or she must overcome to achieve the goal of the story.