The real key to a good interview is preperation and making a good first impression.
Research the company:
No matter how busy you are, if the company has a web site, take the time to review it. Doing research proves that you are engaged with what the company has to offer, and that you made an informed decision when you applied for the internship.
Prepare responses to frequently asked questions:
You can't predict every question you'll be asked, but you can prevent the "ums" and "uhs" through the interview. Articulate ahead of time why the internship opportunity is important to you. You don't have to memorize a scripted response; the key is to have some foucused ideas in your head that will convey your best side to the interviewer.
Bring the paperwork need:
Résumé, Learning Contract Part 1, Learning Contract Part 2, and the Guidelines for Supervisor. This shows that you are responsible and organized.
First Impressions: You only have one chance to make a first impression - make it a good one!
You don't want to be overdressed, but you also don't want to look like you just stepped out of the shower. A general rule is "business casual" which is described as conservative, but still comfortable. Women should avoid clothes that are too tight or revealing, and men should stick to dress shirt and pants. Dressing professionally is always your safest approach unless you are told otherwise.
The eyes become the window into your interest level, confidence and professionalism during the interview. When you establish good eye contact, you'll feel heard and appear likable.
A Good Handshake:
Your handshake should involve strong grip, deliberately pump up and down, and you should maintain eye contact. A lazy handshake makes you appear disinterested, however, don't be overzealous, it's distracting and annoying.
Thank you, thank you, thank you:
It is often overlooked, but the thank-you note is a crutial part of the interviewing process. It doesn't have to be long, put promptly thank your interviewer for his/her time. As with all correspondences to any potential employer, be sure to use correct grammar and avoid informal language.