I work closely (week to week) with about a dozen different writers every year and part of our process is a VERY in depth character bible for any character that makes a significant appearance in a story.

The process works like this:

1. Label the greatest failures and successes in your character's life up to the point in which they enter the story (as they relate to the major issues we all encounter: love, money, family, sex, drugs, art, accomplishments, education, career).

2. Using a narrative approach, describe the events of each and every one of those failures and successes.

3. When you've got 20 pages per character, summarize the major VICTORIES and SCARS of each character on a single page.

The product of this work is your bible; your contract with your character that you will write them true to their own life story.

Throughout the world of your story, your characters are subconsciously chasing the greatest moments of their past to repeat the glory, and running from their greatest failures to avoid the pain.  Great stories arise out of circumstances where a fear has to battle a desire and one has to win at the cost of the other.

For example:

Samantha

Greatest Failure: Dropped out of school.

Narrative description: When Samantha was in the 7th grade her mother was killed in a hit and run car accident. Samantha was the oldest of four children and because her father was passed out drunk, she had to go and identify the mutilated body of her mother.  When she returned home, something clicked inside of her and she realized that with her father as incapacitated as he was, she was the new head of the household.  She faked her age and immediately got a job at a local restaurant where she went every day after she sent her three younger siblings off to school.  For the next two years, she worked her tail off to keep food on the table. Then her father took some pills in a drunken stupor and never woke up.  From there she elevated her game to a higher level, finagled her way into a corporate job with a major theme park and took on the full role of caretaker.  Her siblings are a great personal joy for her, but every day at work, she secretly worries that her lack of a degree will one day be found out and send her life and their stability tumbling down a steep hillside.

Greatest success: Employee of the year

Narrative Description: In her fifth year of working with the theme park she was promoted to a management position, and made responsible for an event that hosted 30,000 guests at the park.  She had to manage the entertainment (a prominent young singer), the catering (over 300 staff), and relations with a VERY picky client who wanted everything done perfectly.  The success of the event earned the theme park a series of very lucrative contracts for the next three years that generated an additional annual $3 million dollars and earned her the coveted employee of the year award, a job she competed against thousands of others to win. To her it meant that she could actually accomplish anything she set her mind to; that she was worthy, and that regardless of her lack of education, she had a place in this world and could compete with anyone, and take care of her family.

Notice that her greatest failure and her greatest success in this area are two sides of the same coin.  This is by design. (Imagine 10-20 pages written out this way that highlight both sides of the coin for her as they relate to love, sex, money, family, etc.)
Now that you have outlined how important her status has become to her, imagine if her "secret" is threatened by another character with equally powerful fears and desires.  How might she behave to protect her secret?

As you can imagine, this kind of work makes the eventual writing of the chapters rather easy because the characters have their own agendas that you have carefully constructed.  I liken it to raising a child and then pushing them out of the nest. You hope you have raised them well, but ultimately, they will make their own mistakes and be accountable to the consequences as they learn how to live and behave and navigate their world.

Spending your time doing this kind of "homework" before writing lends to very powerful interactions between characters, like multiple balls being let loose in a pinball machine.  They ricochet off of one another and are difficult to control, which mirrors life.

Happy writing!