Another good search tip is to let one good book or article lead you to others. Scholarly publications almost always have bibliographies or lists of works cited. These are lists of the resources the author used to write the book or article you've found. Explore these! If the original source is useful to you, works used by the author may be valuable, too.
This technique is referred to as citation chaining. Think of this as a way to locate your source in the web of other research. You can chain backwards by looking up other sources that appear in the bibliography of the item you have. You can also chain forward by locating other sources that cite the item you've found. The easiest way to do this is to look up your item in Google Scholar.