Writing an argument requires you to choose a specific point or assertion and then systematically argue for its truth or validity, justifying your claims with evidence. You can argue for a certain side of an ethical situation, for a certain interpretation of a text, or for the superiority of one thing over the other. To put it simply, you can write an argument for any side of anything that can be argued about.
Keeping your argument clear and organized will lend credibility to what you’re saying, and credibility goes a long way in making a successful argument.
It is okay to bring your opinion into an argument, but only if you support it with other facts, statistics, or outside sources. You need to show valid reasons behind what you’re arguing for—and “because I think so” is not a sufficient reason.
Sometimes it can be a good challenge to argue for the side of an argument that you disagree with, or to create arguments for both sides. And it always helps your own argument if you can show that you understand the “other” side and then show why you think your side is the right or better one.