A viva is not a random collection of questions and comments from your examiners, strung together by whatever you say in response.
Your university has regulations that govern the viva. Your department has expectations for what a good viva “should” be like. By reading regulations and talking to graduates you can build a sense of the pattern – the structure – that underpins your viva.
Your research and thesis are the basis for many areas of discussion in the viva. Your thesis is set out chapter by chapter and it’s natural that your examiners would follow that flow in your viva.
Your examiners will have prepared for your viva too: reading, thinking, writing and discussing what needs to happen. They have their own research and while you cannot predict every question they might ask, you can appreciate from where their questions might come.
The structure of a viva is not a big topic to dig into and digest. Perhaps the most important point to remember is simply this: there is a structure.
The viva doesn’t just happen.