You should write out this information with no structure in mind, simply let the words flow from you. It's intended to allow your mind to be open to whatever inspiration occurs while you think about the character.
Get the information written. Don't edit it. It is not intended to be seen by anyone else. This is information that only the player of the character needs to know
------- Character Questions -------
Who are their parents? Did they know their parents? Where are their Mom and Dad from? Did they work, what was their profession? Who was your character closest to? Mom or Dad? Did they have any Aunts or Uncles? Were the Aunts or Uncles living with the family? Close to the family? Did they know their grandparents?
When were they born? Are they immigrants? First generation? Second? Did they have brothers or sisters? What were their names? How many of each? Where did your character lie in the family tree? Youngest sibling? Oldest? Middle child? Which sibling was closest to your character? What did they do together?
Did the family have a pet? What was its name? What kind of animal was it? Did it live in the house? Who took care of it? Did they have more than one pet? Who was closest to it? When did it die? Is it still alive? Who takes care of it now? Did it have any good/bad habits? What was your character's relationship with the family pet?
When your character was a child what was their favourite thing to do? How often did they get to do it? Were they artistic? Mathematical? Curious? Conservative? Shy? Were they scared of anything when they were young? If so, did anyone help them with that?
What is their health like? Do they have any allergies? Are they robust? Athletic? Frail? What are their personal habits like? Are they clean? Tidy? Well-groomed? Or not?
What were their favourite clothes? What did they like to eat? Were their family meals or did everyone eat separately?
Who were their friends? Who was their best friend when they were nine years old? Around the age of nine-ten, they learned something valuable from their parent. What was it and what happened? Where did the family live? Did they live in a house, apartment, ranch, condo? What kind of things did the family have? Cars? TVs? Rich? Poor? Was the family close to any other families?
Where did they go to school? Who was their teacher? Their favourite teacher? What did they like to study? Were they a voracious reader? Or did they shy away from it? Why? Did they participate in any school functions? Plays? Teams? Clubs?
Around the age of thirteen-fourteen some event occurred in their lives that made them think about what they might do in life. What was that event? How did it affect them? Who else was there?
Who did they date in high school? Who was their favourite person? Who did they stay away from? Why? What was their life like in high school?
Did they go to college? What did they study? Did they get to travel abroad? What was their first job out of college? Was it in their chose profession? Who did they work for? Did they like them? Did they get any opportunities? Responsibility?
If the character is older, you will need to answer more questions.
Did they get married? Who did they marry? How did they meet? What is their family like - the In-laws?
Did they have children? What were the children's names? Are the children still alive? How did having a family effect who they were? Did they change jobs?
How did their career progress? Did they move up? Down? Stagnant?
Is their spouse still alive? What is their job/profession?
Are they still married? Divorced? If divorced, did they/would they get re-married? If so, then to whom?
------- Finish the above questions first, then answer the following:
What is their point-of-view? What is their view of the world? Are they optimistic? Pessimistic? Does the world belong to them? Or does it treat them badly?
Who is/was their mentor? Who is the person in their life who teaches/taught them the most about life? About their profession? About being a person? About being themselves?
What are their professional relationships? In their career/work, whom do they get along with? How do they treat those who work with them? Is there someone's whose work that theirs compliments? Is there someone whose work that theirs is at conflict with?
What is their attitude? Are they dark? Carefree? Sarcastic? Straight-shooter? Hate the world? Love it? What do they expect out of their job? Their relationship? Their life?
What is their Belief System? Do they think that hard work will get them what they want? Do they believe the Universe is a random series of events? Or is it pre-ordained?
Anyway, I could do this all day, you get the idea. Spend some time putting answers to questions like these and you'll have a much better idea of who your character is. Get more invested in them as a person instead of just a concept, and you'll likely be slower to reroll them.