Once you’ve chosen your narrator, your next job is to figure out how they speak. Have a good long think about how their upbringing, social class, race, gender, sexuality, education, job, family home life, nation, etc. interconnect and serve to shape their morals, choices, preferences, and understanding of the world.
Depending on how your plot is structured and the way your scenes are woven together, both your narrative and your readers may benefit from being able to experience your story through multiple different narrators.
"Exposition" can be a scary word. In some writing circles, "experts" will warn you to exercise extreme caution when using it, or they'll make it out to be a difficult but necessary evil. But ultimately, exposition is just another writing tool, and it's used in all sorts of writing, even beyond fiction.