Do your characters come to you fully formed? Mine usually do and I, after outlining the plot, usually just jump write in. The problem is that sometimes I don't know my characters as well as I think I do. I let the plot, not the characters, drive the novel. I have a little exercise that can help.
In the interest of full disclosure, when I first did a project similar to this in my undergrad, I thought it was the dumbest thing EVER, but when I had to teach a creative writing class on characters this past fall, I used the exercise and found value in it.
For the class I taught, I brought in an episode of The Big Bang Theory. It was a grad class, so it was okay to have a show with inappropriate jokes, but for a HS class, I would choose something else. As a group, we answered the questions based on what we saw of Sheldon's character in the clip.
I then had the class answer the questions based on a manuscript they were working on and once done, asked what the easiest and hardest questions were to answer. One person said the hardest question to answer was "who was your character's first love?" and another responded that was the easiest for her. This just goes to show that each character and each story requires different questions. What might be helpful to some is useless to another, so when doing these questionnaires, feel free to skip questions.
To do the exercise, take out a piece of paper and answer any of the following. The first ones are basic biographical questions. The rest are more thought provoking.
2. Hair color
3. Eye color
5. Body type
6. Distinguishing features (freckles, scars, etc.)
7. Special jewelry/watch
9. Phrases frequently used
* the same bio can be done for family members or minor characters. Obviously you can add to the list.
1. Who was your character's first love?
2. In what situation would your character be a hero?
3. What is their biggest fear?
4. What is their greatest desire?
5. How do others view your character? What is his best quality? Worst?
6. How does your character view himself? What does he think his best/worst qualities are?
7. What were or are his career aspirations? (For a teen character, this could be what college do they want to get into etc, or maybe he just wants to pass math. The questions are flexible.)
8. What are his hobbies?
Obviously there are many more questions one could ask, but this is a good starting point. Sometimes when I get stuck in my writing, I ask myself these type of questions about my character to know how he or she would react in a situation.
I am currently watching Alias and saw a great example of this. Marshall is a tech guy, who has never flown. He also has a photographic memory. In what situation would he be heroic? When his photographic memory is needed to remember a code. He did and in the episode he was captured. On the plane, he admitted to having built a parachute into his jacket with a tandem cord. On route to the mission this seemed completely illogical, but by the end of the episode, he and Sydney were trapped and needed it so they could jump out of a 40 plus story window. Not only was Marshall the unlikely hero, but the parachute was a Chekov's gun or sorts. Never introduce something that won't be used.
Do you do character profiles? What questions do you ask?