The general guideline in information retrieval is to use as specific search terms as possible to describe your information need, Also, you have to consider the following aspects:
Mind maps or concept maps are a way to specify and refine the search problem and to determine search terms. For instance, the subject "history of women's education" may be presented as a mind map such as this:
Besides relying on creative thinking, you may also turn to dictionaries, special glossaries and controlled vocabularies to detect suitable search terms. In a controlled vocabulary certain term or terms have been preselected to describe a certain matter or subject. When a controlled vocabulary presents how certain terms are related to each other, it is called thesaurus. Examples of controlled vocabularies are the thesaurus for ERIC, an extensive database for education-related materials, MeSH, a thesaurus in the life sciences, and the Swedish controlled vocabulaty for books, svenska ämnesord.
An example of term relationships:
Context free grammar
Grammar translation method
Controlled vocabularies are an excellent aid in finding search terms and keywords. When using controlled vocabularies, the search is conducted using the same terms that have been used in entering the information in databases. What is more, controlled vocabularies provide related terms and synonyms that otherwise would have been left unnoticed. For an extensive search with the best possible results it is recommended to combine search terms from both everyday language and controlled vocabularies.
From Search Terms to Search Queries
The primary objective in choosing the search terms is to articulate the information need in concrete, specific wordings. These central concepts produce the search profile, which means that the information seeker must define the central concepts of the search topic, possibly find synonyms and equivalents in foreign languages and find equivalent, broader or narrower terms for the keywords. In addition, the information seeker must consider how to combine the keywords in search query and whether to define the search using limiters such as date or language. However, bear in mind that the ways to define the query and possible limiters can vary between different databases.
The mind map that was mentioned above can, for example, be formulated into a following search query:
The next chapter on search techniques will look at how to combine search terms and how to use truncation.
The needed information is not always found on the first attempt. The search profile and search terms often have to be modified during the search. Examining the most interesting and relevant results can prove to be fruitful; more searches can be conducted with the keywords found from these records.
Refinement of the keywords, limiters used in a search, and the chosen database can significantly alter the search results. The use of only one database does not necessarily offer sufficient results and therefore data must often be searched from several other information sources.
When you have defined and specified your topic and chosen the keywords and possible limiters, you may begin the search in database.
Source: University of Tampere: Tampere University library information search guide