I have used letters to the editor of The Ballarat Courier, The Age and the Herald Sun over the years to put a viewpoint I feel strongly about, or sometimes acknowledge policy enacted elsewhere, that I wish to see enacted in my own state.
Most senior school students learn how to use persuasive language effectively, but make sure you have a clear contention, then use techniques like emotive language and rhetorical questions.
Keep your letter short, sharp and to the point and you will likely see it published.
The best day for publication is Saturday, for highest circulation and readership. This means getting your letter off on Friday, especially if it is about a key issue.
You will be required to have your name published and the location where you live.