Venue
Unless you are absolutely sure of the location of the venue for your interview, do a dry run in advance. Find out where it is, available public transport (could be a problem and require a lift from somebody!) and anything else you need to know to ensure you arrive in good time for the interview.
Arriving late will create a bad impression and make you flustered, which will mean that you do not perform as well as you might have during the interview.
Appearance
Try to dress smartly but comfortably and do not worry about appearing fashionable. What you wear when you are socialising with friends is likely to be modern and fashionable but may not strike the right chord with an interviewing panel.
Boys should wear a suit if they have one or a nice shirt and trousers/jeans if they do not. Girls should wear smart clothes and not too much make up.
The main thing is to be comfortable when you are sitting being interviewed. Uncomfortable clothes can distract you and again detract from your performance.
Coloured hair, earrings, piercing, too much jewellery etc are fine for your social time but probably best avoided during the interview.
Timing
Always arrive ahead of your appointment so that you have time to calm down, read any relevant papers (newspaper advertisement for the post, job description etc), visit the lavatory etc.
Do not arrive too early, as the receptionists will usually inform the department concerned who may consider this to be as impolite as turning up late.
Remember the interview process starts the minute you arrive on site so be polite to receptionists and people who are sent to take you to the interview room. Also be wary of CCTV cameras (which may catch you putting on make up adjusting clothing etc.) and speaking critically about the interview panel, the company and/or people you have met since you arrived. That other person may be an employee who could report back on you!
Preparation
It is always a good sign that you have prepared for the interview by doing some research on the employer in advance. Putting any organisation into an Internet “search engine” (Google, Yahoo) will produce some information, which you can read.
If during an interview with say Whitbread, you are asked what the firm does it looks really good if you can mention that apart from their interest in pubs and beer, they also own Travel Inns and TGI Fridays.
Keeping an eye on the business pages of newspapers is also a good way of preparing as recent developments/initiatives by organisations are often published. Knowing the latest news will look very impressive.