Use articles from peer-reviewed journals(see the Evaluating Your Sources tab, above) and books from scholarly (mostly university) presses as much as possible to support your arguments. Some topics just won't work within these limits, but you can usually find and relate some scholarly theory papers to just about any topic with a broader view.
Find the invisible college for your topic-- the cluster of scholars most frequently cited and researching on topics related to your topic. When you are reading books and articles, make a note of the names of authors and research that often gets mentioned in different books and articles. This is the invisible college. Sometimes, articles in scholarly subject encyclopedias can help with getting some names, since the point of these articles is to make you aware of the most prominent research and scholars on a topic. Research Handbooksand Annual Reviews Online can sometimes help identify the key papers and authors as well..