Internships are a tricky thing for both organizations and interns. I have devised a guide, an internship bible if you will, to clarify the boundaries in an internship.
The most important thing to remember is that an internship is suppose to be a mutually beneficial relationship. Both intern and organization should come out of the relationship satisfied.
FOR THE ORGANIZATION:
Thou shall not limit the intern to coffee-runner.
Yes, part of being an intern is doing menial tasks that those working for the organization don't want to do. Sometimes there are copies to be made, envelopes to label, or letters to fold, and that's fine. But making an intern do things completely unrelated to the organization like getting your coffee and picking up your dry cleaning isn't cool. Remember, mutually beneficial.
Thou shall be patient
Its not always easy to deal with teaching an intern, although some are great and very receptive. You have to be patient and understand that in many instances this is the first time the person is getting hands on experience in the field. Take your time, teach them well, and sow the seed for them to be successful at what you are teaching them, in the future.
Thou shall be prepared
I can admit I've struggled with this one myself. You have to have tasks for the intern to do. Devise a plan, make a schedule, so that the intern isn't just taking up space, and wasting both of your time.
FOR THE INTERN:
Thou shall ask questions.
Don't just take instructions and complete tasks without thought. The purpose of an internship is to LEARN in the field. Ask questions, ask WHY things are done a certain way, or HOW the system in place came to be.
Thou shall exceed.
Doing only what you are told is limiting yourself, and not taking advantage of your internship opportunity. If you are an intern you are at a unique place. You get experience in the field, while still having the leeway to experiment and make mistakes. In a real job you will be completely held accountable for your mistakes, in an internship you get to try things out.
Thou shall be professional
You want to make a good impression on the organization you are working with - with your work ethic, dress, personality, etc. A bad impression on a company who could potentially hire you in the future is a BAD thing.