This questionnaire is found in Gotham Writers Workshops Writing Fiction.
You might start with questions that address the basics about a character:
What is your characters name? Does the character have a nickname?
What is your characters hair color? Eye color?
What kind of distinguishing facial features does your character have?
Does your character have a birthmark? Where is it? What about scars? How did he get them?
Who are your characters friends and family? Who does she surround herself with? Who are the people your character is closest to? Who does he wish he were closest to?
Where was your character born? Where has she lived since then? Where does she call home?
Where does your character go when hes angry?
What is her biggest fear? Who has she told this to? Who would she never tell this to? Why?
Does she have a secret?
What makes your character laugh out loud?
When has your character been in love? Had a broken heart?
Then dig deeper by asking more unconventional questions:
What is in your characters refrigerator right now? On her bedroom floor? On her nightstand? In her garbage can?
Look at your characters feet. Describe what you see there. Does he wear dress shoes, gym shoes, or none at all? Is he in socks that are ratty and full of holes? Or is he wearing a pair of blue and gold slippers knitted by his grandmother?
When your character thinks of her childhood kitchen, what smell does she associate with it? Sauerkraut? Oatmeal cookies? Paint? Why is that smell so resonant for her?
Your character is doing intense spring cleaning. What is easy for her to throw out? What is difficult for her to part with? Why?
Its Saturday at noon. What is your character doing? Give details. If hes eating breakfast, what exactly does he eat? If shes stretching out in her backyard to sun, what kind of blanket or towel does she lie on?
What is one strong memory that has stuck with your character from childhood? Why is it so powerful and lasting?
Your character is getting ready for a night out. Where is she going? What does she wear? Who will she be with?