It may seem the most obvious point in the world, but it can’t be overstated: be early. You need to be ready and waiting the second you’re called in if you want to stand any serious chance of getting the job. Aim to arrive at least 30 minutes early, in case you get stuck in a traffic jam, miss your train, or fall victim to any other transport-related fiasco. If you know you are going to be late, call ahead as soon as possible.
Once inside, if your preparation is solid enough, the interview will to some extent look after itself. Good preparation will mean that you’ll know your answers inside-out, be ready for any tricky ones they may throw at you, and be relaxed enough to have a two-way conversation and ask thoughtful questions of your own.
You should also be aware of your body language. It’s natural to be nervous but try not to fidget or jig because it’s very off-putting to interview someone who can’t sit still. Don’t slouch, and remember to keep eye contact with whoever’s talking to you.
Finally, however much you are warming to your theme, take care not to interrupt or talk over the interviewer – the usual rules of polite conversation still apply.