Use synonyms--try to think of several different ways that your serch term or concept could be stated. Example: multicultural, cultural differences and diversity could all be used for the same concept.
Double check your spelling--if you have misspelled a word your results will probably not be good.
In most databases you start your search using keywords related to your topic in a query box and request a search.The search engine attempts to match the keywords with entries in its database then returns a "hit list" of records related to the keywords. The records in the results hit list are usually ranked by relevance with the best matches at the top of the list.
Your search can usually be improved by using search operators which help make your search more precise. some search operators are so widely used they have become practically universal, these are:
Exact or Phrase search
Trunction or Wildcard
Most search engines provide advanced search feaures where you can refine your search by limiting it to specific fields such as author, title, keyword or by date.
Most search engines have help page for both basic and more advanced searches.