Writing is rhetorical: it is designed speech.
If you are like many of my past students, you might dread the responsibility of making your written work rhetorical. You shouldn’t.
You already use rhetorical choices in your day to day conversations because you interact with a variety of listeners. You wouldn’t speak to a tax auditor in the same way you do to your closest friend. Your boss cannot be spoken to with the same words you would use with a toddler. Your grandmother probably wants more warmth and familiarity from you than from the cashier at the gas station.
Throughout your day you make deliberate choices in your communication. Conversations are as cooperative, professional, friendly, or courteous as the situation warrants. Each time you think about your audience then adjust what you say and how you say it, you are being rhetorical. With your family, you use insider jokes and a verbal shorthand based on your history together. At work, respecting bosses and company rules may mean you need to smarten up the casual talk you use among your colleagues.
In a classroom, you communicate with your instructors using a more formal, subject-specific, technical vocabulary. In a lab session with other students, you keep the precise subject vocabulary needed for the work, but drop the formal tone. In a counselor’s office, your tone might remain formal but your word choice shifts to personal. When you are in the bookstore, your communication shifts entirely to casual. Part of being a good student is learning when to make the needed shifts.
What you can casually do in personal conversations you need to more thoughtfully do in your written homework and exams: weigh what you want to say against how your audience needs to hear it. Design your writing to suit your audience.