1. Listen more than you talk. Soak up information about how the organization works, and the reasons why, before you offer "helpful" alternatives.
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2. Don't segregate yourself with people in your age group. Get to know older workers too. Your peer group may be more fun for happy hours, but those coworkers who are a decade or more older than you can possibly help with your career. (And you might find out you enjoy their company too!)
3. Don't become part of a workplace clique. As much as you might like some coworkers, you should maintain professional boundaries. Don't get drawn into gossiping, and don't take on other people's workplace battles just because you consider them friends. Too many young workers have harmed their own careers by focusing on chitchat over work, or by deciding to dislike the boss just because a coworker does.
4. Take mistakes seriously. There's nothing more frustrating than an employee who made a mistake and doesn't seem to think it's a big deal. When you make a mistake, immediately take responsibility for it, figure out how you're going to fix it, and make it clear that you understand its seriousness. Responses like "my bad" or worse, no response at all, signal that you don't take work seriously.
5. Take notes. Your boss expects you to remember the specific instructions you were given—and that includes nuances, not just the overarching idea. For most people, that means taking notes. And while a good manager is happy to answer questions, she won't be if the questions are ones she already answered when you weren't bothering to pay attention.
6. Don't use social networking sites or instant-messaging with friends throughout the workday. When you're at work, you should focus 100 percent on work. There's no quicker way to make a bad impression than to be spotted on Gmail or IM’ing with friends when you should be working.
7. Do what you say you're going to do and by when you say you're going to do it. Always, always sticking to your word will establish you as someone reliable and trustworthy, someone who is on top of their game—and it's such rare behavior that you'll stand out for it.
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8. Pay attention to the culture. This is hugely important, and when new employees don't do it, they come across as tone-deaf. Observe how others act and you'll pick up a ton of information about cultural expectations. Are people compulsively on time for meetings? Do they take a real lunch or eat at their desks? What hours do most people work? Is there a lot of chitchat during the day, or do people stay focused? Do people primarily use email to communicate or do they talk in person? While you don't need to become someone you’re not, you do want to try to roughly fit into cultural parameters.
9. Be open to learning. You may have learned lots of theory in the classroom, but it tends to change drastically when human behavior gets involved. College gave you theory; work is going to give something entirely different, so stay humble and realize your first job is going to be largely about learning.
10. Thank people who help you. When your boss or another coworker takes the time to help you with something, give them a sincere thank you. People who feel appreciated are more likely to go out of their way for you again. If you don't seem to care, they probably won't bother again.
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.