As part of your viva preparations, make sure you have researched your examiners’ most recent publications. For both external and internal, take a look at their last two or three papers. Get a sense of their interests, the methods they use and the questions they have been considering.
Compare that with what you’ve done. Look for commonalities and differences, and build an idea of what that means for you, your work and your viva. Are there questions you might anticipate? Are there topics in your thesis that you might have to explain to them because they might be outside of their knowledge base?
Read your examiners’ recent papers to gain perspective. You don’t need to become perfectly aware of everything they have ever done or everything they currently do.
A little work will help.