In order to write an essay, you have to have an idea or an opinion on the subject. That is your thesis. Then, the body of your essay goes to prove your thesis. What is your opinion on the importance of politeness, courtesy, in life? It is important or unimportant? Do you think it is over-emphasized or is it that too few people are really polite anymore?
After you've decided on that, the rest of your essay gets easier. You will need facts either from books, magazines, interviews, your own observations, etc. to prove your point. Don't forget to comment on each fact showing how that fact proves your point.