As a professional interviewer I meet people every day in an interview situation and talk with many clients about their experiences. Many candidates who should be well experienced in interviewing still make elementary mistakes that often create a terminally negative impression with the interviewer.

Detailed below are ten classic mistakes that you should try and avoid at all costs and which are in order of importance.

Don’t be cold

Be positive and enthusiastic. Smile, don’t scowl. If you project a cold rather than a warm image this will negatively affect the way people judge your personality character

Don’t come unprepared

It’s imperative that you that you prepare for an interview in the same way you would prepare for an exam. As an interviewer, it’s so obvious when people don’t prepare for interviews as they fail to answer basic questions about their resume and can’t give detailed answers about key elements of their personal history.

This creates two poor impressions. One that your answers aren’t detailed enough and secondly and perhaps even worse that you couldn’t be bothered to prepare for the interview. Research on yourself, your resume, the company, the job and why you are good for it and want to do it.

Don’t dress or present inappropriately

Recent meetings have included a young man who arrived for his job interview with one of my clients almost certainly straight from a night out. He was unshaven and very tired in a crumpled shirt and suit and smelt of beer and tobacco.

My client terminated the interview within five minutes. Similarly I met a lady last week during the mid morning who looked ready for a date with her boyfriend, which is fine for going out but could create a problem in the office particularly in this role which was a managerial role.

Turn off your mobile phone

Keeping your mobile phone on is a very now thing to do but turn it off or put it on silent – not vibrate! If you do forget and the phone does ring just calmly apologies and turn it off immediately without glancing at the caller ID. I interviewed a young lady last month who not only took the call but then proceeded to talk for a minute to arrange a lunch meeting which irritated and annoyed me and certainly prejudiced my view of her.

Don’t be late

Being late for an interview can always happen but if you feel you will be late call ahead and apologise. If you are going to be very late you may need to rearrange the interview for another day to give you the best chance. Whatever happens don’t be late or cancel for a second time or you will test your interviewer’s patience.

Don’t stare out of the window or at your feet

Maintain eye contact and keep your other body language positive. As an interviewer it is unnerving to interview someone who does not look at you and indeed looks out of the window when answering questions. Other classic errors are excessive stretching, yawning or leaning on the desk. By maintaining eye contact you can use your body language to develop a rapport and form a positive impression with the interviewer.

Don’t chew gum

Within the past year I have had to ask candidates to stop chewing gum and have heard from one client who had someone who wanted to keep his iPod headphones on through the interview.

Don’t shrug your shoulders when asked if you have any questions

Again be prepared to ask some questions about the job, the company or the sector or if all else fails about the interviewer. It’s not good enough to say “No, you have been thorough and have answered all my questions” as a good interviewer will interpret this as being under prepared.

Don’t be over made up or wear too much jewellery

And not just the girls! It does of course depend on the job but any role that is a management or professional role you should be understated not overstated.

Don’t be rude or abusive

While you would expect this to be a given, I have had clients react very badly (not surprisingly) to interviewees losing their temper, becoming defensive and abusive within the interview. No matter how calm or apologetic you become the damage has already been done. If you think the interviewer is testing your patience don’t try and take them on, just bite your lip and be courteous and make a mental note to get even by not working with them.

If you avoid making a classic interview mistake, you will substantially improve the chances of you creating a favorable impression and progressing through the selection process. Good luck.