The ethos part, which wins you the "interest and the good will of the audience," as Cicero puts it. (He calls this section the exordium.)
Or statement of facts. Tell the history of the matter or list your facts and figures. If you have the time, do both. This part should be brief, clear, and plausible. Don't repeate yourself. State the facts in chronological order, but don't begin at the beggining of time--just the part that is relevant to the immediate argument. Don't startle the audience with "believe it or not" facts--this part should be predictable. What they hear should sound usual, expected, and natural.
List the points where you and your opponent agree and where you disagree. This is where you can get into definitions as well. It's a biological issue. It's an ethical issue. It's a rights issue. It's a practical issue (what benefits our society the most?). It's a fairness issue.
Here is where you get into your actual argument, setting out your argument packet ("We should do this because of that") and your examples.
Destroy your opponents arguments here.
Restate your best points and, if you want, get a little emotional.
Before you begin an argument, first determine what your audience is thinking. You need to know its beliefs and values, the views it holds in common. The common sense of your audience is square one--the beginning point of your argument. To shift people's point of view, start from their position, not yours. In rhetoric, we call this spot a commonplace--a viewpoint your audience holds in common. You can use it as your argument's jumping off point.
We equate a commonpalce with a cliché, but the terms once had a broader connotation. The rhetorical commonplace is a short-form expression of common sense or public opinion. It can range from a political belief (all people are created equal) to a practical matter (it's cheaper to buy in bulk). Commonplaces represent beliefs or rules of thumb, not facts; people are created equal only if you agree on the definitions for "created" and "equal," and it's not always cheaper to buy in bulk. A commonplace is not just anything that pops into a person's head, however. "I'm hungry" does not represent a commonplace. But "When I'm hungry, I eat right away" is a commonplace, as is "When I'm hungry, that's good: it means I'm burning fat." Different groups (such as healthy eaters and dieters) have different commonplaces. In fact, people identify with their groups through the groups' commonplaces. These attitudes, beliefs, and values also determine a person's self-identity--the assumptions and outlook on the world that define an individual. We will delve into identity later; right now, let's look at the commonplace as the starting point of rhetorical logic.