Giving generalised answers: It is important to be specific in answering questions about your behaviour. Examples you give should be concrete examples from the past.
Using ‘we’ rather than ‘I’: When you say “we” it can cause uncertainty about your role in the situation you’re describing. When you say “I”, it seems more authentic and the interviewer can relate it to you much more easily. If you mean “I”, say “I”.
Being under-prepared: It will be obvious if you haven’t done your research on the organisation or the position.
Being over-prepared: Warning! The answers you prepared are not the preparation, practicing generating answers is. Very often candidates present a well-structured, well-worded answer which does not address the question. Listen to the question, pause and then select from the examples (not answers) you have mapped out and then answer the question that was asked.
Getting too nervous: The context of an interview may make you nervous, but it’s important to remember that it’s only a conversation, and that you’re evaluating them as much as they are evaluating you. Don’t waste time worrying, focus on your preparation.
Saying too much: Be careful not to explain your project it in its entirety and then get back to answering the question later. Make your answers complete, but concise and relevant. Always err on the side of brevity and offer to give a fuller explanation on each part.
Saying too little: Always offer to provide more detail. Always assume that the interviewers know nothing of the project you are speaking about and never assume that they have no interest in the subject area of your answer.
Not dressing for success: It is important to feel good for the interview so don’t be afraid to show your personality. At the same time it is important to look the part of your position: smartly dressed, meticulous grooming etc. There is no excuse for poor presentation. It only demonstrates that you are not willing to make an effort for this position.
Criticising former employers: No matter what they did or didn’t do, never criticise your former employers. You may see potential for improvement but direct criticism is not relevant and shows a lack of loyalty and tact. You also don’t know—the interviewer and your current boss could be having coffee tomorrow.