Begin outlining your novel with pre-writing exercises such as mind mapping or clustering. Create a plot line revealing the shape and actions of the story from beginning to end. Transfer the plot line onto a large space, giving each section or chapter its own cork or dry erase board, or paint a wall with chalkboard paint and write the entire plot line there. List all major and minor characters. Allow space for all subsequent character notes to be visible and easily found.
Write a character study for each character on your list. Stop writing the novel to create a character study for those unexpected characters who come up as you write. Write about the character's job, where is he from, what he does for fun, what he looks like and how he reacts to various situations. Know your characters in much greater depth than what is actually displayed in the novel to know how they will react to the novel's conflict, interact with each other and alter the momentum of the plot.
Jot down notes and ideas about characters, their development and their relationship with the plot, as you write the novel. Using sticky notes or index cards, assign each character his own color and keep your character notes color-coded accordingly. Place the notes under the pertinent sections of your plot line. Make a map of characters' interactions by drawing lines or running yarn between corresponding character notes.