Find your argument in a newspaper editorial page. It is better to use an editorial than an op-ed, by the way, because the arguments are generally tighter and more recognizable.
When selecting an article, scan the article and determine what the conclusion is before deciding whether to use that article or to find another one. Do not just select the first article you find: make sure you know what the conclusion is before you begin to work on your paper!
When writing your paper, first state the conclusion, and clearly indicate to me that it is the conclusion. Then, list the premises as P1…, P2…, etc. Thus:
Conclusion: Golf should be illegal.
P1: Golf is unhealthy.
P2: Golf promotes drug abuse.
P3: Golf is immoral (or whatever).
This list must be the first thing in your paper. Do not write an introduction or anything else above the conclusion and list of premises–begin your paper after the list.
Your paper will then evaluate the argument according to ALL of the elements in the prompt: clarity, credibility, relevance, completeness, and overall strength. You MUST clearly indicate which element you are evaluating at which time, using the five words listed above to let me know where I am in your paper. The purpose of this paper is to take something in ordinary langage and render its structure clear; if I get lost reading your evaluation then you have not completed the assignment sucessfully.
Finally, your paper must include a link to your source, and it must clearly state, apart from the link, the title of the editorial and the name of the journal or syndicate from which you got it.