Finding your character’s voice is one of the hardest things to do. Learn everything you can about your imaginary friend, not only how they look but how they feel. The feeling will give you a clue as to how the person will act. Think about how the person would act if they lost their job or spouse. How would the person behave if they caught someone in a lie? What religion is the character? How much money do they have? What is the level of education? All of these factors will color how they behave in certain situations–and how they speak. These elements will feed into creating a believable character with a distinctive voice.
I believe you must intimately know the character’s hopes, desires, emotional conflicts, and goals. Humans are complicated. There are good and bad elements in every personality. In a story, you must find and expose both sides of the person. Put the character in a situation to win or lose depending on two opposing choices. For example, if the person fights a certain enemy will the character also go to jail, or lose the love of his/her life?
Know the character as well as you know yourself, and you will probably create someone we want to get to know better.
Keep writing. We welcome your comments below on finding your voice.