Read the research question carefully. Which words can be used as search terms? Are there alternative related terms and similar concepts? Think what sort of vocabulary is used by authors writing on the topic e.g. women or female rather than ladies.
Too many results? Look at the advanced search and refining options available such as limiting by date, abstract and/or title.
Some databases will automatically look for UK and US English spellings e.g. organise or organize. They may also look for variant word endings. Look carefully at results to see if this has happened. If not consider using wildcards to indicate to the database to do this e.g. estimat* will look for estimate, estimates, estimation, estimating etc.
Use quotation marks to make words appear next to each other in that order e.g. “big data”.
If you want words to appear near to each other in any order use a proximity search e.g. in Scopus cyber W/6 security will look for the words cyber and security appearing within 6 words of each other (check the search help in each database to find out what the operators are – in EBSCO it is N/n).