Let’s start with the obvious. Assume that everything you write can be broadcast to the world. Even before blogs and Facebook, this has been the case.
When I was a cub reporter, an elderly homeowner sent me a letter she received from her neighbor, who happened to be an attorney. She was involved in a property dispute with him, and this letter threated the woman with endless legal action that would haunt her every waking (and sleeping) moment.
I persuaded my editor to print the letter as part of a story on the case. The fallout was amazing. The community rallied in support of the elderly homeowner, and the attorney was inundated with hate mail. He apologized and dropped the suit, and undoubtedly lost a ton of business—and sleep.
Nowadays, the homeowner wouldn’t even need to persuade a reporter to do a story; she could just post it to Facebook and let everyone’s outrage do the rest.
Here are some other basic tips that can save you from being the (unflattering) talk of the Internet.