1. Playing online during the workday. If you’re logged into Gmail chat all day, doing your holiday shopping online, or playing on Facebook when you should be working, it could cost you your job. Your employer has the right to monitor anything you do on your work computer, including checking your personal email. Never use your work computer for anything you don’t want your boss to know about—whether it’s job-searching, online shopping, complaining about your job, hanging out on social networking sites, or anything else.
[See The 50 Best Careers of 2011.]
2. Complaining about your boss. You never know who might be listening, and if you get a reputation as a complainer, your boss will eventually hear about it.
3. Not owning up to mistakes. Everyone makes mistakes from time to time; what matters is how you handle it when you do. If you don’t accept responsibility or—worse— try to cover up that a mistake was made at all, your boss will likely be far more angry at this than at the mistake itself.
4. Being preoccupied with whether something is your job or not. Protesting that something isn’t in your job description is a good way to lose the support of your boss. Job descriptions aren’t comprehensive, and most people end up doing work that doesn’t fall squarely within that job description. (That’s what “and other duties as assigned” means.) People who balk at this often end up at the top of a lay-off list. You want to make yourself more valuable to your employer, not less.
5. Getting angry at work. It’s normal to occasionally get frustrated at work, but it crosses a line if you’re yelling, slamming doors, or snapping at people. It only takes one incident like this to get a reputation as the angry guy who no one wants to work with, and that’s a label that’s very hard to shake.
6. Letting work fall through the cracks. If you don’t do what you say you’re going to do—whether it’s as small as responding to an email or forwarding a document or as big as meeting a project deadline—your boss will conclude that she can’t count on you to keep your word.
7. Doing only the basics and not anything more. Doing a merely adequate job isn’t enough these days. With so many qualified job seekers available for hire, you need to go above and beyond in order to be seen as valuable to your boss. If you’re simply meeting minimum expectations, your boss can quickly find someone who will do more.
8. Caring more about having friends at work than about doing a good job. It’s great to get along with the people you work with, but if you’re chit-chatting when you should be working or gossiping about the boss, your bonding sessions may quickly leave you without a job.
9. Taking feedback badly. If you get upset, offended, or angry when your boss gives you feedback on your work, you’re making it hard (and painful) for your boss to do her job. Worse yet, she might start avoiding giving you important feedback that you need to hear.
10. Hiding things. Hiding things—work that isn’t getting done, an angry client, a missed deadline, the fact that you don’t really know how to use that software—is one of the worst things you can do on the job. If your boss isn’t confident that you’ll give her bad news directly or be forthright about a problem, you’ll destroy her trust in you.
Alison Green writes the popular Ask a Manager blog where she dispenses advice on career, job search, and management issues. She's also the author of Managing to Change the World: The Nonprofit Leader's Guide to Getting Results and former chief of staff of a successful nonprofit organization, where she oversaw day-to-day staff management, hiring, firing, and employee development. She now teaches other managers how to manage for results.