Using quotation marks in your query ensures your results contains words and terms you search. Instead of searching for the words individually (think "Diet" "Coke") it will search for them together ("Diet Coke")
Using an all-caps AND, OR, NOT, you can link terms.
AND is a great way to pair two different search terms (think "United States of America" AND "Unemployment rate").
OR searches for both terms ("United States of America" OR "U.S.A.").
NOT excludes terms ("United States of America" AND "Unemployment rate" NOT historical).
Check out the filters on the left side of the search tab. Especially make use of date and subject.
These databases are a great place to start as they cover a wide range of business-related topics. They provide access to scholarly, peer-reviewed journal articles as well as some non-journal content (company profiles, industry profiles, market research reports, SWOT analyses, country reports, etc.).
When searching for case studies, use the advanced search tool and select "Case Study" as a Document Type. If this option is not available, try including it as a keyword or subject term in your search. e.g., case studies AND management