AND - To combine descriptive keywords, use AND. This will narrow a search in which both terms must appear in the results.
NOT - Use NOT to filter out terms that aren't relevant to your search. This will help you focus your search.
OR - When you're looking for synonyms, OR comes in handy. This will extend your search and give you more options.
To narrow your search to a certain category, use Advanced Search.
Author search: Enter one or more names in the "Return articles authored by" box to search for specific authors.
Journal title search: Enter the journal title in "Return articles published in" box to search for journals either by full title of abbreviations
Phrase search: Enter terms in the "with the exact phrase" box to search for the exact phrases. You can also use quotation mark to specify an exact phrase you want to search for or exclude in the other boxes.
Search for your terms anywhere in the full article or limit your search to terms in the title of the article.
Source : Google Scholar Search Tips (https://scholar.google.com/intl/en/scholar/help.html#searching)