There aren't necessarily rules when it comes to writing an opinion/editorial (op/ed) piece. Unlike other journalistic articles, you don't need a nut graph, an inverted pyramid, or other things. If anything, it might look more like an essay or letter than a typical news article. However, there are a few things you can keep in mind when writing an article to make it readable and intriguing.

• Make it timely - Op/eds are usually interesting because they pertain to current events, not something that happened months ago. Connect it with a story that's in another section of the paper simultaneously, or even a letter to the editor.
• Make it relevant - Of course residents will be more likely to read an op/ed if they can relate to it, or if it's about something that's happening near to their homes or their hearts. And for that matter, understand your audience; do they mind reading longer pieces with more facts and substance, or do they want something that's more concise and to the point?
• Make it well-written - No grammatical or spelling errors, lack of structure, and so on. People should be able to read it without stumbling over unnecessary blunders, and a well-written op/ed will garner greater credibility.
• Make it focused - Don't go on tangents and lose readers with a plethora of points and anecdotes. Stick to one argument and persuade readers of it!
• Make it unique - Don't just give dry facts and statements. Be creative (without going overboard and making it unreadable). Are there personal stories you can use? What about your writing can you use to make your op/ed individual?
• Make it factual - Back up your opinion with research, statistics, quotes, and more. Add support when you can to show that your standpoint is reasonable and even true. Prove that your opinion isn't unfounded and preliminary.
• Make it fair - People aren't going to want to read something with slurs and inappropriate comments. You should have a strong opinion that people can determine from the article, but you don't want to call someone out without support. Avoid libel, of course.
• Make it honest - The best writing comes from the heart, so find topics that actually mean something to you, that you can write about with passion and understanding.

Here are a couple of op/eds I've written:

Does your busyness serve a purpose?

Vogue cover offensive to some

I am NOT a crackhead felon