1. Thinking that because you have your degree, you shouldn't have to do grunt work. Most recent grads start at the bottom because that's how you learn how a business works, regardless of your particular degree. You must learn how to write the sort of memo your boss wants to read, how to navigate office personalities, how to simply get things done in an organization. Even if you're not given the most glamorous work, you can pay attention to detail, follow instructions, and care about quality--eventually someone is going to let you do something more interesting.
2. Not being thorough. In college, you could (and were often expected to) argue one point of view. At work, you're expected to consider all the options thoroughly and make a recommendation that includes pros and cons. I often see new grads simply not being thorough in their thinking. Poke holes in your recommendation before you take it to your boss. That way that she doesn't have to.
3. Thinking that what you post on social networking sites doesn't matter. At best, being unprofessional on sites like Facebook or Twitter will limit your professional growth and change the way your boss sees you; at worst, it can get you fired.
4. Procrastinating. If you waited until the last minute to do a project in college, you were the only one who suffered. At work, if you put off a project until the last minute and then you're sick or something else gets in the way, you risk your professional reputation.
5. Not putting effort into forming relationships with older colleagues. You might be more comfortable spending all your lunches with people in your peer group, but then you'll miss out on the chance to form relationships that can help you progress faster in your career. Get to know your older colleagues.
6. Not saying "thank 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 is the author of Managing to Change the World: The Nonprofit Leader's Guide to Getting Results. She is chief of staff for the Marijuana Policy Project, a nonprofit lobbying organization, where she oversees day-to-day management of the staff as well as hiring, firing, and staff development. Her writings have been published in the Washington Post, the New York Times, Maxim, and dozens of other newspapers. She blogs at Ask a Manager.