|Here are a number of questions that you should be able to answer about all of your main characters, even if the information never shows up in your script. These are not all the questions you can ask and answer about your characters but this will definitely provide you will a solid foundation to develop and create them.
What type of birth did they have?
What year were they born and where?
What makes them laugh? Cry? What makes them sad? Angry?
How do they make a living?
How do they feel about their mother? Father?
What sport(s) do they love to play? Watch?
What is their favorite movie? TV show? Music?
What is their favorite color?
What is their favorite food? Beverage?
What is their political affiliation?
Do they gamble?
Do they have kids? Do they like kids?
Are they married? Have they ever been? Do they believe in marriage?
What religion are they?
What is the most exciting thing that ever happened to them?
What is the most traumatic thing that every happened to them?
What type of house or apartment do they live in? How is it furnished?
Do they have any physical diseases? Disabilities?
Have they ever been in love? With whom and when?
Where and when was their first sexual encounter?
If they could change one thing about the world what would it be?
What was their most recent dream?
Do they smoke or drink alcohol? Do they use drugs?
What are three character flaws?
What is their goal in life?
What is their strongest physical attribute?
What do they like most about their body? Least?
Who in the world would they change places with if they could?
Who do they idolize? Worship?
Are they aggressive? Passive?
Do they read the newspaper? Books? Magazines?
Who is their favorite actor and or actress?
What animal would they choose to be?
How do they dress?
How do they show or protect their feelings?
How do they feel about death?
How do they get along with other people?
How did their father influence them? Their mother? Their siblings?
Do they have a brother and or sister?
Was their childhood strict? Lenient?
Were they overprotected? Did they feel rejected? Loved?
What was their families economic status?
Are they smart? Intelligent? Savvy? Slow witted?
Did they go to school or are they educated? High school? College?
Did they like... school? Their teachers? Their classmates?
Do they travel? Where? Why?
Do they have friends? Who? Why? How did they meet them?
What are their hobbies? Interests?
Do they have an imagination? Do they daydream? Worry? Stress?
What is their outlook on life? Positive? Negative?
How do they deal with hostility? Negativity? Ridicule?
What is their health like?
What is their self image? How do they feel about their own size? Looks? Weight? Height?
What's their voice like? Shrill? High? Low?
How do the gesture? Weakly? Vigorously? Controlled? Compulsive?
Are they energetic? Sluggish?
Do they work out?
How do they feel about the opposite sex? The same sex?