Build a character from scratch.
Basic details of who are they? (Age, name, hometown, gender)
What do they want most?
Who or what is standing in their way? What do they want? Why don’t they want this character to get what they want?
What’s their family life like?
Build this character until they are completely and totally fleshed out. Then, make a few more characters the same way. Write their story(ies).