Dress appropriately:
You do not want to arrive for your interview in just jeans and a t-shirt. In all likelihood, you should be wearing formal or at least business-casual attire.
 

Be Prepared:
Do your research on the job you want. You do not want to arrive at the interview without at least a foundational knowledge of the company or what the position actually entails.
 

Make a good first impression:
Give a strong handshake when you enter the room and carry yourself with confidence. Always maintain eye contact with the person asking the questions. If there is more than one person, spread eye contact evenly across the room.
 

Speak clearly:
There is nothing worse in an interview than someone who mumbles their replies. Take a few seconds after being asked a question to collect your thoughts and then give your answer. Try and avoid saying any filler words such as "um" or "like."
 

Bring extra documents:
It is smart to have a few extra copies of your résumé and cover letter on hand with you in the interview. That way if you reference something on it during your interview, you can distribute the document to the interviewer if they do not have a copy.
 

Ask questions:
Always come prepared to ask questions in the interview. However, topics such as pay and benefits should not be brought up by you. These two topics should be addressed only by the interviewer. Your questions can range from learning more specific details about the position, to a classic question such as, "Is there any reason why you would not consider me for this position?"
 

Send a thank you note:
Sending a thank you note to your interviewer can help to make a big difference. Just because you are no longer in that room does not mean you are not being evaluated. Check out some tips on how to write a thank you note for an interview here from Gettysburg College.