First resort: Library Catalogs and Discipline-Specific Databases (especially those which include abstracts or summaries)
Items that appear in these resources have often been fully described with subject terms, local availibility, and abstracts or summaries which allows for better discovery and easier evaluation.
Last resort: JSTOR, Wikipedia, Google, Google Scholar, the Open Web, Ebook collections, etc.
Freely available resources have less search capabilities and are generally of lower scholarly value. Typically time is wasted looking through too many, less useful hits. JSTOR and ebook collections available through the library, such as Cambridge, are scholarly, but they are full text without description and searching often results in too many hits to easily evaluate. Last resort approaches should be used when you're completely stumped or you're at the final stage of research and ready to find every last thing on a topic.
Never hesitate to Ask a Librarian for advice on searching.
Almost all catalogs and databases have a single search box called "easy" or "quick" or "Siimple Search" and another option called "Advanced Search" which has three boxes and lots of other options.
Often the options of the "Advanced Search" will prompt you to design a more efficient and fruitful search.
Almost all library catalogs and databases allow the use of quotation marks which keeps the words together as a phrase. Example "The Oxford Classical Dictionary." Searching by this phrase results in fewer hits and better than searching on those words separately.
Another incredibly powerful feature is truncation which allows a system to search for variants of a word. Example: laugh* means the system will search for laugh, laughs, laughing, laughter, etc.
keywords = more hits & sometimes worse
subject words = less hits & better
keyword = the word is found anywhere in the item--title, author, abstract, summary, notes, description, publisher, and sometimes full text when it's available
subject words = library catalogs use Library of Congress terminology; most databases have their own terms, sometimes called descriptors, which are often similar but not exactly same as library catalogs.
A good rule of thumb is to pay attention to the subject words in your results and use them to refine your search strategy.