I know someone who applied last year - he didn't get in, but I can give you some tips from what he told me about it. For your interview, make sure you're up-to-date on current events and can express and justify some kind of opinion about it - they might ask you stuff like what you think we should do about the refugee crisis, etc (though that might be only if you're planning on taking Politics like he was). Make sure you have a solid knowledge of your GCSE curriculum (especially math!) for your subject specific interviews - do some revision beforehand. You can't really do much to prepare for the Verbal Reasoning (maybe look online for some papers), and I think they put your interview performance over the score from that test anyway.