All of the above, and this: do your preparation at home. The last really good job I landed I used a one page table which I worked out on the word processor of all the jobs & experience I had which was relevant to this job along the top row, and the essential and desirable criteria of this job down the left hand column. I then put a tick in the boxes of whichever jobs related to those criteria.Then, in the interview, if one of the questions related to one of these criteria I just looked across the row and said: "When I worked at XYZ I did blah blah blah, and this is what outcomes I achieved". (Outcomes and achievements are very important.)
I also had a second page of my strengths and also my weaknesses (now referred to as "challenges") which I rephrased into positive statements, e.g. "I am working on being more systematic to improve my time management skills".
In that same interview I had one of those plastic refillable pencils and the top part swivelled around the bottom half. I discovered that day that I could be sitting there with my hands hidden by the table swivelling that pencil like crazy, letting out all my fidgeting and nervousness but none of the movement showed above the table. I used it deliberately as an interview aid after that.
Having a really well-written Resume/C.V. which states your experience and capabilities helps you to keep a straight face when you are telling them your strengths as well.
By being prepared beforehand you increase your chances dramatically in the interview itself. Find a good trusted friend to help you rehearse your answers too. Someone who will give you sensitive but constructive feedback, someone who has experience as an interviewer or who is good at analysing verbal messages.
Go get 'em, girl!
Helen