I base many of my characters on actual people and define them by their unique traits. The voice of a character must be powerful able to stand alone without having to keep inferring that the character is speaking by using his name. The language choice needs to define him or her.
Allowing the characters to show their frailties is pivotal to the credibility a character will have. An example a women loves to eat lemon poppy seed muffins at Christmas she drinks a couple glasses of wine or maybe a little more and is slightly intoxicated arrested and charged with dui and drugs opium. Obviously, opium was not consumed, but guess what happens when you have lemon poppy seed muffins, yes a false positive.