University of Texas Professor Owen Williamson suggests various approaches, such as comparing the author's findings with public or expert opinion, describing the consequences of accepting or rejecting the article's recommendations or urging the reader to personally take action. Many persuasive pieces use one of the last two methods. A long article with large amounts of data might use the conclusion paragraph to summarize the most important information and describe its significance. This helps the reader to make use of the data even if he lacks a technical understanding of the subject.
Adding a poorly-crafted sentence to the conclusion paragraph can leave readers confused and ruin the article's intended effect. Don't introduce any new concepts, ideas or jargon in the conclusion paragraph. It's fine to summarize the article's information, but don't repeat the same phrases. For example, in a piece describing the features of laser printers, it's better to summarize the features into major advantages and disadvantages in the conclusion rather than simply restating the main features in different words.
Ensure that you base the conclusion paragraph upon the information provided in other parts of the article. It's acceptable to introduce one or two easily-understood facts in the conclusion, but don't wait until the end to provide the most important information. In a promotional article, it often proves most effective (especially for expensive items) to put the price in the conclusion paragraph so that the reader learns the cost after reading about appealing features of the product or service.
Basically, a conclusion paragraph should serve the goal of the article by summarizing its information in a way that promotes the desired action or helps the reader comprehend the main implications of the data provided. Writing a conclusion in this manner will leave the reader with a clear understanding of the article's content and a readiness to put it into practice.