Before you start searching for literature, you need a clear, well-formulated research question, or series of questions. Start by doing a a quick search of OneSearch to get a feel for the amount and type of literature you may find.
The search terms or keywords will need to take account of:
Also consider that the field you search in a database will affect the number of results you retrieve.
In many subject areas, especially psychology, health and medicine, you are expected to use the thesaurus or system of subject headings in the databases. These systems of subject headings are valuable because:
They use consistent terminology. So articles which talk about cancer or tumours or leukaemia will be mapped to the Medical Subject Heading [MESH] term Neoplasms.
They have a tree structure. So you can look up Neoplasms as a MESH term and you will see that if you explode the term you will search for all the cancers in one go.
The subject headings chosen reflect what the article focuses on. So an article of 8,000 words might be given 20 headings in MESH.
If you already know of some good papers in your area (“citation pearls”), look them up in a database and see what subject headings have been applied. They may help you construct your own search strategy.
There's more about using a thesaurus in the database guides which you’ll find in the online help available within each database
If you are expected to retrieve all the literature on your subject, you should use a combination of thesaurus terms and free text or keywords. This is because (a) the most recent items may not be indexed yet; (b) the concept you are studying may not be in the thesaurus; (c) indexing changes over time; (d) errors in indexing do happen.
Ways in which you might limit your search