One important detail in discerning whether or not the content you're reading online is fake not fact is who authored it.
First, look at the byline: Is the author's name given? Without the name of the author it's difficult to determine where the content came from, and whether or not the author is a credible source on the topic. If there is an author or byline given, consider the author's credentials. Does the author have appropriate degrees or professional experience? Does the author disclose whether or not he or she may have a conflict of interest (the author of health-related content, for example, may be qualified to review a new drug, but did the author also receive research funding from a pharmaceutical company manufacturing the drug)? Know who your source is.