There are many things you can do to make an argument strong in a paper. In light of this, let me give you three points.
First, to inspire confidence that you actually know what you are talking about, you need to know the debate extremely well. You need to be able to know all the points better than your opponents. If you can do this, then you will be well on your way in writing an excellent paper.
Second, you need to have a strong thesis of why you believe in what you believe. In other words, you need strong arguments to support your thesis. This the most important point. The stronger your points are, the more you will convince people that you thesis is cogent.
Finally, you need to anticipate the opponents counter-arguments. If you can do this, this will show that you really thought about the issues and that you are a thoughtful person.