The problem with keyword searching is usually that you find too many sources, not all of which are useful. As you begin to develop a set of usable keywords, here are some suggestions for targeting your search in more precise ways.
Boolean Operators are terms or symbols that will allow you to designate specific relationships among keywords. Different databases indicate Boolean relationships in different ways: some require words (either capitalized or not), and some use symbols. Check the help screens for the database you're using to find out what terminology it uses.
Combining Keywords with OR
Combining Keywords with AND
Searching for Phrases
Combining Keywords with NOT
Using Truncation and Wildcard Symbols for Variant Spellings and Word Forms