1. Air private grievances in public Want proof that being a jerk on Twitter is tantamount to being a jerk in real life? Look no further than serial entrepreneur and Dallas Mavericks owner Mark Cuban. "How do they not call a tech on JR Smith" Cuban tweeted angrily during a game last March when a referee's calls didn't go his way. The NBA fined him $25,000 for the digital outburst.

2. Diss your customers Earlier this year, a PR executive named James Andrews tweeted about a certain city: "I would die if I had to live here!" He discreetly did not mention where here was, but he did not think about the fact that he was en route to a meeting with a major client, FedEx, which promptly issued a statement in defense of its hometown, Memphis. The lesson: Think about the context of your tweets, not just the content.

3. Screw up the etiquette "HI TWITTERS. THANK YOU FOR A WARM WELCOME" wrote Oprah Winfrey in her first-ever tweet. Twitter users gasped. Writing in caps is the equivalent of yelling online. Do it only when you are actually angry. But don't get angry on Twitter. (See No. 1.)

4. Get too personal Look, everyone has different standards of decency. There have been tweets about giving birth, undergoing surgery, and everything in between. We're not going to judge you if you reveal too much about yourself (OK, maybe a little). But your employees, customers, lawyers, and kids will. So be careful.