Analyzing the Audience
Whether comprised of one individual or many, an argument is always written to an audience, so it makes little sense to begin without first figuring who the audience is and what they want or expect. This can be done with a little analysis.
As a concept, it sounds pretty simple: Think about who is going to read your argument and why, and then write in a manner that will most help them comprehend the position you are taking. Easier said then done. It turns out that writing-and revising-for a particular audience is much harder than you think. It requires audience awareness and analysis.
The first thing you will need to find out is why the instructor is having you write the paper, and to whom. Sometimes you will be asked to write as if to a larger audience, but for most assignments you will be writing to your professor, an audience of one.