Network.
As a young professional, your main interest should be meeting people who can provide you with information about your future profession. Build professional relationships with your supervisors and other managers in the organization and learn about their experiences. One way to do this is through informational interviewing.
Take initiative.
Don't wait until someone hands you something to do. Seek out opportunities to learn as much as you can! Complete small tasks quickly and ask for more challenging tasks. Don't turn down any assignment because you think it is beneath you. Remember, you are there to learn all aspects of the organization. However, you may volunteer to help with projects that interest you. Ask questions!
Meet with your supervisor.
If your supervisor does not seem to make time for you, don't take it personally. She/he may be busy with other work commitments. Take the initiative to schedule meetings with them. It's important to let your supervisor know what you have accomplished and to be able to ask questions. Be sure to get a final evaluation at the end of your internship.
Be professional.
Arrive at work on time (preferably a few minutes early) and resist the temptation to leave early. If you will miss any work, call in prior to your reporting time. Respect the employer's dress code. Use your time efficiently—minimize breaks and lunch hour, and avoid gossip and office politics. Never do homework on the job. Avoid making personal calls.
Don't be afraid to ask questions.
Always remember that an internship is a learning experience for you. While the employer expects to get a certain level of work from you, you are not expected to know everything. Seek advice and raise questions whenever you encounter something that is not familiar to you. Be open-minded about new ideas and procedures—remember that you don't know everything and that your professors didn't teach you everything.
Do your best work.
Ensure that all work assignments are accurate and completed in a timely manner. Take your position seriously, whether paid or unpaid, and when asked to perform menial tasks, do so without complaining. Supervisors need to know that you are capable of small tasks before they can trust you with more responsibility. At the end of the internship, always leave on good terms. Even if you have a bad experience, never burn your bridges, because you do not know when it could come back and hurt you!