Thinking up the right search terms is one of the major parts of your search strategy.
Go looking for corresponding terms for each part of your search question. Don't forget:
- ​synonyms (house / dwelling)
- broader terms (university / higher education)
- narrower terms (children / toddlers)
- related terms (training / coaching)
- antonyms (terms with opposite meanings, such as parent/child or poverty/wealth
- persons and organisations of importance to your subject
- terms indicating space and time (for instance eras, centuries, names of places, countries)
- avoid bias in your search terms, it might colour the outcome of your search
And also think of the different word forms:
- singular/plural
- verb conjugations
- nouns/adjectives
- different spelling (labor / labour or organisation / organization)
- abbreviations
- translations into languages which are relevant to your subject and discipline
Correct your search terms along the way. If you do so from the very start, you will soon see which (new) terms produce the right results, and which terms don't. Repeat this method as long as it takes.
You don't have to reinvent the wheel. Use resources:
- words from an exploratory search from, for instance, Wikipedia or handbooks
- words from earlier found sources, for instance words from the title or abstract or keywords given by the author
- dictionaries
- thesauri (overviews of selected words or concepts and their mutual relations within a particular field of interest or discipline, often included in large, subject specific databases)