1. Exploit good bibliographies. If there's a great book or article related to your topic, check out what that author cited. If you find a source that is highly relevant to your topic, search for it in Google Scholar and use the "Cited By" link to find out who has cited it since it was published. Literature reviews and bibliographies from recent dissertations can also point you to seminal books and articles on your topic.
3. Make the most of the library's databases. Google Scholar and JSTOR are places to search a very wide range of literature, but the library also subscribes to many subject-specific databases that will restrict your search to only political science, or other social science sources. See the scholarly journal article tab for links to these.
4. Don't wait until the last minute. Start to develop your topic/bibliography now so that you have time to request any materials you might need from E-ZBorrow/Interlibrary Loan.
5. Make a research appointment with the Political Science Librarian for one-on-one help.