Research your topic thoroughly. If you're writing about the main reasons for the Civil War, visit your library and get a few books which give detailed information on the events which led up to the war. Also talk with some history and political science professors about this subject, and look for some credible TV documentaries on the causes of the Civil War.
Support your thesis with credible research. If you're arguing that welfare reform isn't working because there is still not enough vocational training for people who left welfare over the past 15 years, use recent scholarly articles, interviews with economic experts in your city, nonfiction books on welfare reform and if possible, random interviews with local residents who recently left welfare but are struggling to find and maintain decent employment.
Pay attention to formatting guidelines. If your professor wants you to write the paper in APA style, visit your library and print out a few pages of a reference manual that shows researchers how to write papers in this format. Also look at online sites from universities which feature tutorials on APA-style writing.