It can be confusing to know where to use quotation marks. Writers are familiar with using quotes for sentences but what about thoughts? What about words with anothermeaning? This is simply a question of style, and what country you live in. The British do it opposite of Americans.  Single or double quotation marks denote either speech or quotation. Neither style—single or double—is an absolute rule, although double quotation marks are preferred in the United States. (grammargirl.com)

A few general rules:

1. For quotes within quotes—“Why did she call the man a ‘traitor’?” 
2. For ‘scare quotes’ —terms used in a nonstandard, ironic, or other special sense.  Quotation marks used around a word or phrase when they are not required, thereby eliciting attention or doubts.

“Putting the term ‘global warming’ in scare quotes serves to subtly cast doubt on the reality of such a phenomenon.”

1. If you have a scare…