First off, check all the module paperwork for guidance notes.
Then a few days beforehand, do a really thorough read through. Note any typos and missed references. Note key sections + page numbers. Make sure you come across as knowing your thesis really well.
It can be difficult to predict questions. Your supervisor should be able to advise. Any significant weaknesses in the work are likely to be mentioned, so if you can address those sensibly if asked, that's a good thing.
One if the purposes of a viva is to establish that the work is your own, so make sure you are all over it.