One little word, "audience," means so much. Our subject (and topic), our method, our organization all depend on who is going to read our piece of writing.
Right now, you probably write assignments for the teacher and, no doubt, to please yourself.

Tonight we will practice writing for two different audiences.

Considering Audience

What are your audience's interests? 

What does your audience know? and not know? 

What might your audience want to know? 

What do you know that might interest your audience? 

How will you write for your audience?

Assignment 

Write two paragraphs about a unique cultural event (such as a celebration that is done only by those who share your culture).

First, write a paragraph about this celebration for someone who shares your culture.

Then, write a paragraph about the same celebration for your teacher, who you assume does not know anything about it.

See a teacher writing sample: Being the Tooth Fairy