Be persistent in your searching.
Try both keyword and subject searching.
Narrow a search by using subject headings. Locate subject headings by looking at the descriptors associated with pertinent articles and books.
Try these tips to narrow your search.
Try both singular and plural forms of words. Use an "*" in Academic Search Premier to get a variety of word endings.
If searching a compound word, try it as one word and as two words (e.g. rain forest or rainforest) to see which retrieves the most useful results.
If searching a term with an internal dash, search the term in each database with and without the internal dash (e.g. x-ray vs. x ray) to see which retrieves the most useful results.