Too many results?
Review your search results and look for off topic entries. Is there a word that consistently retrieves irrelevant results? Type that word into a new search box and use the Boolean Operator "NOT".
Not enough results?
Think of other ways that you can describe the topic and combine them with the Boolean Operator "OR". Remember to use parentheses around your "OR" grouping.
If you still aren't sure, ask a librarian.