1. Don't wrap up your ego in your artwork. People are going to criticize the work you do. Learn from those people.
2. Engage your peers and learn from them. Every artist knows something you don't. A tool, a tip, or a technique. You only have a limited amount of time to learn these things from them (before you graduate, one of you changes jobs, etc.) The best way to learn these things from others is by sharing what you know. Don't hoard.
3. You can only grow so much through school and work. The best artists hone their skills outside of school and outside of work. They keep creating even when they're not "on the clock."
4. You will not enjoy every task/assignment you are given. Some you will like. Some you will hate. As a professional artist, you will be gauged on your ability to execute both types with the same quality, efficiency and dedication. Half-assed work, regardless of preference, is still half-assed.
5. Learn to communicate with others proactively. If someone tells you what they want, and they walk away without you having enough information, it's not the other person's fault. If there is information you need, it is your responsibility to obtain it. If you start working with incomplete or inaccurate information, you're probably going to end up doing the job twice. Ask the questions you need to ask. The flipside of that argument is true as well. If you foresee a problem or think that a peer or manager doesn't have enough information, then it's your responsibility to voice your concerns.