Connect your keywords using Boolean operators (AND, OR, NOT). Find different words variations using truncation, and use quotation marks to keep phrases ( i.e. "public health") together in your search.
Use OR to broaden your search.
For example, if you search advertising OR commercials, you will find articles that include either term.
Use AND to narrow your search.
For example, if you search advertising AND commercials, you will only find articles that include both terms.
Use NOT to exclude results with certain words.
If you search advertising NOT commercials, you will find articles that include the word advertising except for those that also include the term commercials. In Google, use a minus sign instead of NOT (e.g. advertising -commercials).
Use a truncation symbol (the asterisk * is the most common) to look for different word endings.
You do have to be careful with truncation. Sometimes you might get unexpected results.
Use quotation marks to search for a phrase (two words or more).