woman looking at her facebook page (Photo: Brendan O'Sullivan; Getty Images )

One wrong tweet, and you could lose more than just a few followers--you could lose your job. In March, two developers were fired after one of them took to Twitter to complain about sexist jokes that the other had made at a tech conference. The male developer was fired because of his comments, and the female developer appeared to be laid off due to the harsh backlash she and her company received in response to her tweets.

Whether these employees should have been let go is debatable, but the incident is a good reminder that companies are keeping tabs on what you post online--and they can punish you for it. "Social media is not trivial anymore," says Miriam Salpeter, author of Social Networking for Career Success. "We have to realize that even though something may seem like a throwaway comment, people are listening."

So how can you make sure that your social networking habits aren't screwing with your career? Start by avoiding these major mistakes:

Mistake #1: You don't know your company's policy
More businesses are adding social media stipulations to their employee handbooks, says Mike Haberman, human resources consultant for Omega HR Solutions. So now might be a good time to actually read all that paperwork you received when you were hired. Even if your employee handbook doesn't specify that you could be terminated for a rogue Facebook post, that doesn't mean you're off the hook. Companies will often find a way to fire someone if they feel it's necessary, says Salpeter. Most workers are employees at will, which means they can be fired at any time, for any reason, she says. So it's crucial to know what might get you in trouble before you do it. If that's not outlined in the handbook, schedule a meeting with HR ASAP to find out what the policy is.

Mistake #2: You stir up controversy
Advertising your political or religious beliefs on Facebook and Twitter is practically the norm these days, but these types of posts can backfire at work, warns Salpeter. After all, if something seems offensive to your HR department, it could result in a reprimand or even a termination. And it's not just the usual hot-button topics you have to worry about. Even something that you don't automatically view as controversial--like following Chris Brown on Twitter or posting about sexual health rights--can affect someone's perception of you. And when that person has the power to fire you, you definitely don't want to come off as offensive to them.

Mistake #3: You're overly negative online
You wouldn't go around the office ranting and complaining all day, so don't do it online, either. HR may see a string of rude or angry comments as a red flag--whether they're work-related or not. "You're demonstrating your temperament and your attitude," says Salpeter. So keep the hate-tweets and humblebrags to a minimum, especially when you're applying for a job.

Mistake #4: You accept your boss' friend request without a second thought
While it's generally not a good idea to seek out your boss on Facebook, it can be tricky if your boss friends you. If you haven't yet found yourself in this position, you can change the settings on your profile to make it completely unsearchable and explain to your coworkers that you're just not a Facebook person. But if a colleague's friend request is already pending, the best you can do is clean up your profile, accept their request, and be hyper-vigilant about what you post in the future. To be on the safe side, consider everything you post online to be public, even if you've set up tons of privacy settings.

Mistake #5: You treat all social-networking sites the same
If you're trying to maintain a strong personal brand, you need to be active on a variety of social media sites--but not all of them have to be associated with your work life. If your tweets and Instagram posts tend to be frivolous, that's OK--just don't list your job or company in your bio, says Haberman. You should, however, focus on beefing up your LinkedIn with professional contacts. You may also want to customize the URL so that it ends with your full name (just go into your profile settings--it's free and easy to do). That way, your LinkedIn will be one of the first things people see when they Google you.
The key: using good judgment when you decide what you want to post and where is the most appropriate place to post it. "What's more important to an employer than someone who knows how to exercise good judgment?" says Salpeter.