Or even set up an account. Don’t let an ill-advised tweet cost you your job or harm or destroy your career: @Etiquette @Etiquette@FirstAid:
Rebecca Hiscott says at Mashable: 

Even if your Twitter account is private, the web has a sneaky way of spreading unsavory information to the public. Treat your Twitter posts as though your parents, grandparents and bosses were reading. Meaning, keep the profanity to a minimum, be thoughtful and respectful of other users, and rein in your netspeak and abbreviations ("LOL" is fine — "omg jus chkd out th3 n3w Hmeland ep its kool" is infuriating).

Whoever pieces this together had better find out something interesting, but they probably won’t.
From Twitter Etiquette For Dummies:

Some Twitter users are considered noisy because they tweet so much, whereas others can come across as standoffish because they don't tweet frequently. A good rule when you're starting out is to post at least four or five tweets per day. You'll most likely find yourself tweeting much more often than that, but if you aren't yet fully comfortable with it, use that number to get started.

Best to tweet four about news of interest and one about oneself, many say.
From Social Media Today:

1. Should I follow every one who follows me?

Think of Twitter “follows” as valentine cards at grade school. You don’t want to be the person who gets all the valentines but gives none in return. Know why? Because it isn’t social — and you’re engaging on social media when you’re on Twitter. Being “cool” was fine in school — but on Twitter it really only works for celebrities. (I’m still waiting in vain for Lenny Kravitz to follow me back.)

And lastly, from Huffington Post, all tips in 140 characters or less:

For a while I enjoyed my local anonymity because I was able to express opinions on topics I never would have addressed in a Sunday sermon or Wednesday night Bible study. But as my local readership increased, I began to rethink my previous reckless "opinionating." [More.]

If there is any chance that a tweet will put you on the street, a good question to ask is: Why does the world need to hear from me on this? Sadly, most career-ending tweets are not valiant stands for truth, but stuff better left unsaid. Knowing the difference makes all the difference.
 So don’t let a tweet put you on the street. Let it put you in the driver’s seat!