When I say courtesy, you tell a reader the best possible story you can. You never at your critics, or even your fans, if they disagree with you or say that your story sucks. And when you are writing, you ALWAYS try to write a good story.
You are your story's first reader. Are you writing this story to please yourself- to explore an idea, take yourself on a trip into another person's head, or to attack a frontier no author has attempted? Are you uncomfortable with your preference for tied-up detectives- and tackle it in fiction?
If you are a writer, an idea won't always be fun to explore. You may write yourself into a dark alley with a serial killer and the heroine has nothing but her hairspray and a big mouth. You may end up in a boring part when the antihero blasts through a prison. But corners do not necessarily mean that you haven't pleased your inner reader. It merely means that your inner writer has gotten in over his or her head, which can happen.
Here is a big no-no, however, no matter what you write: NO SLACKING OFF WHEN CLASSMATES ARE READING!!! If you are taking a creative writing class, your classmates want to assess your strengths and weaknesses while you write and maybe spend a few minutes enjoying a story. When you put no effort into your work, they cannot help you become better writers, and they will know when you haven't gotten into the story. Your inner reader will know, and not care. At least until the criticism hits.
Your inner reader's judgment will fragment. You will stop writing for a few days, or at least throw out a few pages of work. And your inner reader will only come back together when someone says that they like your story and shows you how to make it better. Or if you pick up a new book and cheer up for the next round.
ALWAYS try, at least for the sake of your inner reader. You may not be able to fix the errors in your story sufficiently, but at least you will have tried. And you will be able to trust yourself when you revise.