The best way to avoid the most common and dangerous interview mistakes is to think ahead and decide not to make them.
1. Lying
Although it's tempting, it doesn't work. By all means gloss over the unflattering things. But out-right fibbing NEVER pays.
"If you tell the truth, you never have to remember anything." By Mark Twain
2. Slating your current company or boss
Fed up with your current job and would give anything to leave because they've treated you badly? Your job interview is NOT the time to seek revenge. Bear in mind that the interviewer will be listening to your answers and thinking about what it would be like to work with you. Ask yourself: do you like working with people who constantly criticize others? Isn't it a bit wearing? The trouble is that the interviewer draws massive conclusions from your answers. So your throwaway comment about your boss or employer may be interpreted to be your "standard" way of thinking. It makes you look bad, not your employer.
3. Being Rude
If you find you were accidentally rude, then apologise calmly and genuinely. Then leave it behind you and get on with the rest of the interview. If you dwell on it, it will affect your performance. What's "rude"? Well, that depends on your audience. As a rule of thumb, avoid cracking jokes about potentially sensitive topics and beware of being too "pally" with the interviewer: polite and friendly is enough. After all, you're not in the pub with them. So stay professional. Also bear in mind that everyone you meet could be involved in the selection process. So blanking the receptionist or talking down to the junior members of staff could cost you the job.
4. Complaining
Ok, so your train journey might have been a nightmare and maybe you thought the tube would never arrive, or the tailbacks on the motorway were endless. But your interviewer doesn't want to know that!
Complaining, even in jest, is not a recommended icebreaker. It may be completely harmless, or it might simply make the interviewer switch off. Don't let complaining set the tone for the interview!
5. Talking about people you don't get on with at work
It's common to be asked how you deal with conflict. Companies realize the importance of interpersonal relationships in the working environment. So if they ask you about difficult people or situations make sure you hold back from character assassination and blaming others for problems because it won't do you any favours! If you accidentally do "break" this rule, apologise and explain what you "really" meant.
6. Not Being Prepared
Re-read the relevant version of your CV and the job advert, just before the interview. You'd be surprised how many people can't remember what they wrote on their CV. And if you remember what type of person the job advert was looking for, it's easier to demonstrate that you have those qualities.
Make sure you've brought with you anything you were asked for. It's fine to bring a note-pad and pen, but make sure they're tidy. It's even ok to bring notes with you; particularly if you have any questions you want to ask. It shows you're taking the job application seriously. Ill-prepared candidates rarely get job offers.
7. Appearing to be too nervous, or too confident
If you appear too nervous they'll think you're not confident enough to do the job. However, appearing too confident will make them think you won't fit into the team. If interview nerves are an issue for you, it's worth getting practical help from a professional, such as an interview coach.
8. Making a weak first impression
Unfortunately, no matter how hard the interviewer tries, a lot of "don't want to hire them" decisions are made in the first few minutes of contact. If you make a strong first impression, the interviewer will be more inclined to overlook "imperfections" in your answers.
9. Not having researched the company
As a general rule, the more famous the brand, the more they will expect you to have done your homework. Researching the company shows you're serious about the job.
10. Putting your foot in it and not noticing
Yes, we know, you didn't mean to put your foot in it. But it doesn't really matter what you intended. What counts is how the other person reacts. So what can you do? Be prepared to simply say "sorry, that's not what I meant!" This requires you to actually be paying attention to the interviewer, rather than your own thoughts and feelings. Once you've apologized, leave it there, take a deep breath to help you relax and move on with the job interview.