An argumentative research paper takes a position on a contentious issue and argues for one point of view. The issue should be debatable with a logical counter argument.
Whenever possible, choose a topic that you feel passionate about. Writing about something you enjoy certainly shows in the final product, making it more likely that you will be successful writing a paper about something you enjoy.
Whenever possible, look for peer-reviewed empirical research. These are articles or books written by experts in your field of interest, whose work has been read and vouched for by other experts in the same field. These can be found in scientific journals or via an online search.
With a topic selected, the next step is to begin research. Research comes in numerous forms including web pages, journal articles, books, encyclopedias, interviews, and blog posts, among others. Take time to look for professional resources who offer valid research and insight into your topic. Try to use a minimum of five sources to vary your information; never rely on only 1-2 sources.