Good luck, MowMow!
My advice - rehearse. It may seem awkward, but rehearsing WILL have an impact. Out loud, ask yourself a question. Pause. Out loud, answer the question.
Lists your strengths and weaknesses; be honest. Now turn your weaknesses into a strength. For instance - I'm am very, very detail-oriented. I can occasionally become so focused on getting the minutia of details right that I lose track of the overall picture.
This is true, and it truly can be a problem, but interviewers love to hear it. (Personally, I don't think they actually believe someone can GET that focused on the details so they don't really understand the scenario I'm describing; they only hear "detail-oriented". *chuckle*)
All other things being equal, it's the relationship established between the interviewer and the interviewee that seals the deal. Try to mirror the interviewers state of mind: relaxed, intent, casual, whatever, and, without being a mimic, try to copy their body mannerisms.
Never cross your arms.
If you see an opportunity - which usually happens towards the end of the interview, but not always - try to make a personal connection with the interviewer. Do they have a banner in their office for a team you also like? You could make a comment about the team's current progress in the sport. That kind of stuff.
Oh, and make sure you have a question or two about the company, something that fits in with or potentially impacts what you're going to be doing if possible. Of course, you'll have to know some history to do that, but you should anyway if you want to work for them.
Good luck, again!