What's the best way of preparing for an interview?
Interview preparation is very important and although you may only use part of what you prepare at least you can do well with those questions.
Prepare well before hand, don't leave it to the last minute. Then you can use the night before to refresh your memory. Use the information you have to hand, normally the job advert and perhaps a job description.
These should guide you to the organisations requirements so write the sort of questions you would ask if you were interviewing, then write you answer. It's also worth researching the organisation, be familiar with their products (or work area), any big competitors and if they have been in the press recently for any reason.
Interviewers don't expect you to know a lot about the organisation but they do expect you to have done the basics.