Time and again interviewers ask the same general questions in addition to those of a more technical nature. Learn them, prepare your answers, and practice them on friends. Common questions are "Why are you interested in this position?" "Tell me about your current boss". "What are the most satisfying/frustrating things about your current employment?" "What are your strengths/where do you think your weaknesses lie?" "Why do you think we should give you this job? "Where do you see yourself in 5/10 years time?"
People shouldn't judge a book by its cover, but they do, all the time. If you look untidy that's how you'll be remembered and first impressions really do count. Always wear a suit and tie or neat skirt/dress and polish your shoes. Even if you are attending a second interview and you know the organisation allows less formal work dress, maintain a professional/formal approach, as you don't know who you may happen to meet, the Managing Director perhaps! It may sound obvious, but be civilised and remember your manners. Shake hands firmly with people you are introduced to and when you leave.
Find the right tone in which to present your positive aspects. You have to talk about your achievements to show you are the right person but do it without being boastful. Under no circumstances should you spend a significant portion of the interview running down your current employer - this is viewed as negative. Don't wait until after the event to decide that you wished you'd tried harder to get the position. Always go in with the intention of getting an offer, only then do you really have the chance to weigh up how this opportunity compares with others. Many people, with the benefit of hindsight, have regretted they didn't take a particular interview sufficiently seriously - don't let yourself be in this "if only" category!
Turn weaknesses into strengths
Don't pretend you have no weaknesses because everyone has some. On the other hand don't put your self down, because you could be talking your way out of a job. Discuss your weaknesses as though you have recognised them and strive to overcome them. "I used to have bad time management, now I prioritise my workload first thing every morning". "I like to take control and be involved in everything. I sometimes find it hard to delegate but when I have the results have been positive."