oh I know so well how you feel - mine was just a week or two ago.......
apart from reading my thesis and some articles (new and already included), I actually have done most of the work in the last 10 days following my mock-viva, in which I also felt to have answered poorly and that I should say so much more. However, at some point after that in the preparations I decided to keep it 'simple' and basic. The important point is to answer the questions with some confidence - not to have the most scholarly and rhetorical performance and to come up with this and that. Your thesis and what you did is the point of reference. This helped me a lot, because I felt less under pressure to 'shine' and to say tons of things.
The best preparation for me was to think of a short summary of what I did in 2-3 min.; my original contribution to the field, both empirically and conceptually; my major findings; conclusions; and implications for the field.
A common question perhaps even before your contribution is about your doctoral history, what brought you to the topic.
Then another common area of grilling is your theoretical framework, why you chose it and then your methods, what are the core methods, their strengths, weaknesses and limitations.
Apart from these typical areas, be prepared to be challenged on pretty much any of your decisions, try to think of your work and what you did from someone else's perspective who would have done things for whatever reasons differently, it's not that they necessarily disagree but the defence is what its name says. It helps to get yourself into the mood of critically examining what you did in order to be able to explain 'why'.
What examiners really like is if you somehow bring their own work into play, and if it is only one point of a recent article or so ;-)
Sorry if you knew all this already.... it was just a very good recepie for me to have this basic structure prepared and thought through, good luck!!! (up)