The examiners generally aren't there to catch you out, but they will rigorously assess your knowledge and defense of your thesis. I don't think even the most confident of people cruise through their viva, everyone will have wobbly or waffly bits. However, if you really prepare, you'll probably have 70% of it nailed.
There are specialist viva courses in most unis. However, some do seem to place emphasis on viva horror stories - that rarely happen. Your university should also offer interpersonal skill courses and public speaking courses.
Books? I can't really think of any specific ones. Rowena Murray writes a lot on vivas - see this article and references therein:
http://education.guardian.co.uk/egweekly/story/0,5500,1042654,00.html