Character interviews are a very open, flexible way of building a character. It helps develop their psychology, voice, their memories, and even material to be used in your book all at once! However, many interviews I have seen left me disappointed since they either explored superficial details (”What’s your favorite ice cream flavor?”) or asked way too open questions (”What was the happiest day of your life?”). I made my own and my interview’s been a great help in building my characters.
Following Along
Write your answers as the character, in first person. I used to do them in 3rd but I find 1st person to be closer into the mind of the character and it also gives you an opportunity to develop their voice. Even if you're writing in 3rd i recommend this, as you get to know your character from a completely new perspective. Not every question will strike gold with every character, so if you can’t think of anything, just skip it.
Making Your Own Questions
I really encourage you to do this as you get the hang of it! I would recommend asking questions that can lead to deeper psychological threads, or at least interesting moments in their past. For example, “What’s your favorite ice cream flavor?” is both very specific and superficial. A better substitute would be “What’s a food you have strong memories attached to?” since that can lead to a character discussing their backstory, or even worldbuilding details on what dishes exist in your world. Honestly, think of questions that you would be able to give a good answer to. A lot of questions are anchored somewhere in a potential source of either conflict or desire, as well as how they might go about resolving that. Even more good info might come from what they do in their average life, as you can fill in the gaps of what they do everyday and make them feel more human.
The Document
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