Use truncation to search for variations on words, e.g. leader* for leader, leaders, leadership; terroris* for terrorist, terrorists, terrorism. Many databases, including the catalog, use *. Some use ! or other symbols.
More keywords to use--also may be used as descriptors (subject headings) in some databases:
Target your search by using Boolean operators--AND, OR, NOT--to combine the terms you want to find.
Unlike Web search engines, some databases will read a string of words as a phrase. By tweaking your search intelligently you will avoid the "overload of hits vs. I-didn't-find-anything" syndrome.