Quotation marks should only be used if you are actually quoting someone else’s work or words. They should not be used for emphasis or to distance yourself from the text. The exception to this is shortform works, such as article or chapter titles. It is best to avoid all special formatting to add emphasis, as your writing should be strong enough not to need this. However, if you feel you absolutely must emphasize something to stand out, use ‘single quotes’ to differentiate from actual quotations. An example of this error would look something "like this."
The reasoning behind this rule is to ensure strong writing is being developed and used, and to increase readability for your audience. When quotation marks are misused, a reader can become confused as to what work is yours and what comes from an outside source.