What brings a very good impression on the interviewer? A good way is not to be nervous when you go to the interview. Even if you have not practiced much, or only know a little about the company, just be ready when you walk in. It will make the employer think you're ready to go, or that you have to polish a little as a person. This will make you look a little more mature, and could convince the employer you would be the type of person who could go live from day one.
When you enter the interview, do not be afraid to talk and ask questions. If an interviewer that brings someone you know or a situation that has been before, do not hesitate to speak. It's only going to help if you have connection, or may show a little bit of experience you have. It will go a long way forward to the list of potential candidates to fill the vacancy. Not only that, but if you say something relevant, you are rooted in the interviewer's head.
Not only act as a professional, dress like a pro too. Make sure you are wearing a suit and tie, even if you go through a part-time job. Just because you could wear a shirt and shorts at work, you can never hurt to dress for the interview. This shows that you take the interview seriously, and will most likely take your work seriously as well. A shirt and trousers are a must, and a tie is a nice touch too.
Make sure you do not smell bad or have something stuck in your teeth. You want your interview to be based on merit, not something stupid you did. It has much to gain if a connection is lost by having a piece of spinach in your teeth or a bad smell. This will make the interviewer think of you in a negative way to look at your resume for a second interview.
Simply go to your interview as you would have any other meeting for the first time. Be polite, respectful, and be prepared to enjoy a pleasant chat with the interviewer. Do not do too much and just make sure you do nothing to take the mixture. You cannot get a job with the first interview, but you will be missed in the first interview.