I do this too. I actually have an entire worksheet I do for it. I've never finished one of the worksheets, but I've gotten to a point where I feel like I have a good understanding of the character. I'll post it in case anyone wants to use it. The document itself looks a bit better with bullets and formatting and all that crap, but that's it.

Character Development Worksheet From Hell
Personality:
Name?
Nickname?
Preferred name?
Date of birth?
Gender?
Fears?
How do they react when they’re afraid?
Are they more likely to fight or run?
Why is their fear a fear of theirs in the first place?
What mood are they usually in?
What makes them laugh?
Overused words or phrases?
Are they prone to curse?
How do they see themselves?
How are they seen by others?
Are they competitive or more laid back?
Do they think before they make decisions or to they shoot first and ask questions later?
How do they react to praise?
What are they most likely to be praised for?
How do they react to criticism?
What are they most likely to be told off for?
How often do they cry?
Do they have a philosophy?
If so, what is it?
What do they stand for?
Indoorsy or outdoorsy?
What’s a nasty habit of theirs?
Will they ever stop?
Is it bad enough that they need to stop it?
Which of the five senses do they rely upon most?
Which of the five senses do they rely upon least?
How do they treat their superiors?
How do they treat those lesser than them?
What do they value in a friend?
What is likely to earn someone their distaste?
If they could change something about themselves what would it be and why?
What were they like as a child?
Do they like animals?
What’s their favorite animal?
What’s their least favorite animal?
Did they grow up rich or poor?
How has money, or lack thereof, molded their life?
Will money change them? If so, how?
What is the most offensive thing they’ve ever said?
Did they mean it?
If they could, would they take it back?
Do they feel bad for having said it?
Would they say it again?
Was it said to the subject’s face or behind their back?
What was their best childhood memory?
What was their worst?
What have they done that they’re most ashamed of?
When were they last devastated by something?
What was that something?
What accomplishment are they most proud of?
Do they boast of it?
Have they ever saved anyone’s life?
Has someone ever saved their life?
Do they believe in love at first sight?
Why or why not?
Have they ever been in love?
With who?
Has their heart ever been broken?
By who?
Why?
What is their sexuality?
Are they open about it?
Do they fight more with violence or with words?
What is their greatest weakness?
What would they do if it was ever exploited?
What is their greatest strength?
Is it a hidden strength or an obvious strength?
Do they view their greatest strength as a strength?
How do they react to social drama?
Are they more likely to cause drama or to smooth it over?
What is their main phobia?
What is their weapon of choice?
Have they ever been bullied?
How do they react to others being bullied?
Where do they go when they’re angry?
What do they do there?
How do they view freedom?
When did they last lie?
What do they most often lie about?
Do they consider an omission of truth to be a lie?
How often do they make promises?
Do they ever make promises they can’t keep?
Do they ever do so knowingly?
Do they keep their promises to the best of their abilities?
Who is their hero?
Why?
What’s their favorite childhood story?
Why?
Do they believe in happy endings?
Do they believe in a higher power?
Why or why not?
Do they have empathy for others?
Are they easy to anger?
What is a subject that is wise to avoid around them?
Why is this a touchy subject to them?
How will they react if they’re forced to face the topic?
Do people fear them?
Why or why not?
Should they be feared?
Why or why not?
Do they take advantage of the fear of others’?
Do they have secrets?
What are they?
Does anyone know their secrets?
Why or why not?
Are they manipulative?
If so, why?
Are they easy to manipulate?
If so, why?
How many people are in their family?
Is their family close?
If not, why not?
Are there any wedges between family members?
If so, what and who are they?
Is their family loyal to one another?
What does their family fight most about?
What are their flaws?
Are they aware of these flaws?
Are they willing to try and improve these flaws?
Are they ashamed or accepting of these flaws?
Are they shy or outgoing?
What are their goals?
Short term?
Long term?
What do they do for fun?
What do they believe in?
Are they an introvert or an extrovert?
Are they cautious or careless?

Appearance:
Age?
How old do they look?
How old do they act?
Eye color?
Hair color, length, style, and texture?
Height?
Weight?
Skin tone?
Skin type? (oily, dry, etc)
Face shape?
Distinguishing features
Scars?
Birthmarks?
Physical handicaps?
Predominant features?
Dress
What do they commonly wear?
What do they hate wearing?
What would they always wear if they could?
Jewelry? If any what pieces and why? If none then why not?
Are they hard on their clothes or does their wardrobe last?


Habits:
Good habbits?
Bad habits?
Hobbies?
Hygiene?