The interview questions will be based on the Company's competencies. These will be listed in the Job advertisement, usually 5 or 6 listed. So ensure that you answers can be linked to to the competencies. Give sensible well thought out answers based on your experience. Use the "STAR" Technique for planning the answer, 'Situation' following through to Result". This is what will impress them - that you have prepared for the interview.
It sounds a bit simplistic: but listen to the question being asked AND answer that question - sticking to the point and don't go off at a tangent.
Try not to get too nervous, if you've prepared for the interview,you will be in a better position. Interviewers are looking for the best person for the job. They are not out to trip you up.
Be punctual and smartly turned out.
If you ask questions, make sure the answers haven't already been answered during the interview. This can be a problem with prepared questions. It looks as if you weren't paying attention during the interview. Good Luck.