A good story writes the way the main character thinks. So for example, if your character was intellectual you would use more sophisticated words and sentence structures in and out of personal text. If he was under privileged and uneducated, you would use the respective structure and words.
This is done many time is some of the most popular and well know books of history. Just do what you think is right for you.
English
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My character doesnt have much character then. ._.
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Then create your character the way you feel it should be. You are the writer.