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: 
Your problem may stem from the fact that you are writing a book too much "by the book." Characters aren't like bits of code. Unless they walk around in your subconscious, speaking and breathing and acting like real people, they won't seem like real people on the page. If your characters don't surprise you, they won't surprise anyone else. Novels are about people, not structures, and as a novelist your job is to find a structure that fits the people in your story, not the other way around.
I find a really usful way of getting characters to feel more alive and realistic is to write a character centric synopsis for each significant character.

It's easy to let characters that aren't currently involved in the story you're telling just kind of langish in limbo until the plot requires them again - this can lead to them re-entering the narrative a bit 'out of sorts' 

By writing the whole plot from a given character's point of view you get a much better if idea of what they are up to when they are 'off screen' and this helps make them far more interesting when they're 'on-screen' 

You don't need to write in nice fancy prose, as that can take too long, but in enough detail to fill in the gaps in thier experience. Often you'll find characters that are absent for large parts of the plot, and so you make up something for them to be doing in the mean time - then when they meet up with the plot later, you know what they've been up to - you know how they're feeling about things and this can colour thier reactions etc. 

Also this is usful for ensuring that they know what they need to know - you can have meetings between characters 'off screen' and decide what was said and done - it never makes it into the final novel per se, but working through those interactions in detail really fleshes out the characters and makes them more real when you come to write about them in the actual plot.