The number one mistake that you can make is that you go to the interview late. If you are late, you are not showing you will be on time and responsible. Also, that you have wasted the interviewer's time and they will not be forgiving of it. As soon as you make it there they will show you back out the door. The second mistake is looking like you are going to a fast food restaurant. First impressions are everything and if you fail that, then you do not have a chance. It shows lack of respect not coming dressed up accordingly. Third mistake would be not having constant eye contact. As employers, they know that people get nervous but if you can't seem to be able to look at them in the face to talk, then you will not be able to do your work if you can't do this simple task and it shows respect when you do so. The fourth top mistake would be for you as a potential employee is to not listen to the person doing the interview and talking in turns. If you can't listen then you are in big trouble and it shows you will not have the attention to do the work that you need to do. The fifth mistake to avoid during an interview would be not that thanking the interviewer for their time to do the interview. If you can avoid these five things during your job interview you are that much closer getting that job.
There are some questions that you should avoid, for example, you should not ask what the company does or what you will be doing. You should know what you are applying for and be qualified to do so. You should not ask if you will have to take a drug test. That raises a red flag with employees and chances are, they will put your application and resume in the trash. If you are a smoker you should not ask about smoking policies. The interview is not the time to ask about this policy. If you get the job then you can read the policy manual or ask. The interviewer will remember you from the time you walk in until you walk out their door and the best way possible to get the job is to give them the best impression of you possible.