You can potentially save yourself a lot of time and frustration in the library by developing a search strategy before you even begin your search. For example, you may be looking for information on a literary character in a biographical source when an index would yield better results. Do not forget to check the card catalog as well, especially for older books. Not every book is in the online catalog yet. Try using different search terms, or try a different index altogether.
Coverage typically varies from one index to the next.
If you find one good article, check for subject headings associated with that article. If you are still having trouble locating useful sources, see a librarian for help. As you conduct your research, look for opportunities to expand your list of potentially useful sources. One good way of doing this is to look for a bibliography or list of works cited at the end of books and articles that address your topic. You may begin to identify a particular author or work that is consistently cited.