There are several ways of expressing your opinion. One is to write a letter to a newspaper.
You need to address your letter to the editor. The editor reads the letters and decides which ones to publish. You should feel strongly about a topic or an issue. Keep your letter short and to the point. In the Letters to the Editor page of a newspaper, sometimes there is an exchange of correspondence. People will respond to a letter sent in by someone else. Your letter can be about a Hong Kong issue or a general issue.
Read the following exchange.
Letters to the Editor
Tuesday
Sir
I am writing to complain about people who smoke in public places in Hong Kong. The smoke gets in people's eyes. This can be very annoying. Also, when I get home after a walk in Central, my clothes smell of smoke. This costs me money as I have to clean my clothes more regularly.