In a persuasive paper, articulate a goal to address a public need. For some it is easier to think of this as a problem that needs to be solved, either wholly or partially. You will then vigorously argue for a policy (or solution, if you prefer) which reflects the most efficient and effective way to achieve that goal.
For example, you might have the following as your goal: America needs to become more energy independent, relying less on the importation of foreign oil than we do at present. In your research, you might have encountered and considered a range of policies: Tax breaks for companies developing new fracking techniques and technologies; reduce the number of restrictions and regulations currently impeding off-shore drilling; open the Arctic National Wildlife Refuge, etc. The question to be answered then is this: Which one of these policies most effectively (in terms of results) and efficiently (in terms of cost, time, political feasibility) achieves this goal? Why is it better than the other alternatives?
As you organize and write your paper, keep the following in mind:
Defining the goal or problem should take no more than one-and-a-half to two pages of your paper. For example, if you are writing about childhood obesity, then you should take no more than of the paper to define or outline the problem.
Proposing a policy (or solution) which addresses that problem should make up the bulk of the paper. That is, the majority of your paper is not spent in convincing the reader that there is a problem. Rather, most of the space should be used to convince the reader that your approach is the right one.