Imagine you're an underwater archaeologist. As you search the sea bed, you find an artifact---a piece of tile or part of a jar. Do you stop searching and move to another location? Of course not. You continue working on that area, believing that you are likely to uncover more or related materials. The first artifact you find is only the beginning.
One of the best and most efficient ways to locate additional resources on a topic is to "mine" the bibliography of a book or article. After you have located a useful article, book, or book chapter, review the bibliography to locate the sources used by the author. Then, as you find items from the bibliography, review the bibliographies of those items for additional sources. It is highly possible that you may track back through numerous authors before reaching a "primary" source. By noticing which articles or books seem to be used by numerous authors, you can gauge which titles are considered "important" or authoritative on the topic.
While more traditional searching using a search engine or catalog will be useful, considering trying this bibliographic mining strategy as part of your research process.