I used to interview people in the forces so here are some tips I found useful...
-Practice! Practice general questions with anyone who will help, You can get friends or family to ask you things.
-Present yourself well - Sounds obvious but if you feel good you will perform better. Shower/shave etc in the morning beforehand.
-Mannerisms - If you know you have mannerisms try and control them, nothing can distract an interviewer more than arms flailing and thumbs twiddling
- Posture - A fairly important aspect, you should try and relax, sit up in the chair, don't cross your legs! Keep your body 'open'. If you can feel yourself getting fidgety bend your toes in your shoes.
- Eye Contact - Try and look the interviewer(s) in the eyes, it shows confidence, don't look at the floor or out the window!
- Speech - Speak clearly, concisely and do not answer questions with just 'yes' or 'no' (unless they are obviously after just those answers!, i.e "Have you done drugs?" "No")
- Don't waffle/dig yourself a hole - Seems fairly obvious but so many people do it, remember the interviewer will have your application forms in front of them! Stick to the truth, if you just don't know an answer to a question have the integrity to say "I'm sorry I don't know". If you start to dig a hole, stop and compose yourself.
- Preperation - Goes hand in hand with practice, prepare well, the old saying "failure to prepare is preparing to fail". You have a good idea of the questions coming your way in the managers interview and structured interview, so study your answers. Study a bit each day. If you can try and think of a question for the interviewers, but make sure it is pertinent.
Practice, practice, practice, practice, practice..........