The PhD experience is a very individual one. Each person has their own project, their own methodology, their own timeline, and, in the end, their own thesis. Though other people are also going through a PhD, they have their own individual journeys and things will never be exactly the same for any two people. So too with the viva (I've been told).
We've been lucky in my department. Very few people have had an awful experience. Partly this is because external examiners are chosen very carefully. A good external and make a viva and a bad one can break it. I know I have a great external (and a good internal, for that matter, though I didn't get to choose). That is the first hurdle out of the way.
The second is writing a good PhD thesis. I think I've done this, but I also know, without a doubt, that there are issues. There unanswered questions or things I probably should have done differently. Every PhD has those, though, and they don't mean it's a bad thesis. Knowing what they are and acknowledging them is a great first step. It means fewer surprises in the viva!
I also know that the viva is as much a mental thing as it is a physical event. I have known a lot of people to freak out before their vivas, convinced that they've ruined their thesis or made so many mistakes there's no way they'll ever pass. I've known others that have torn their research in two, looking for all the things they might get called out on. It's hard not to do any of those things. We're sort of conditioned towards it. It's not easy, critiquing one's work, but you do get good at it while writing a thesis.
The third thing about having a good viva is to just be prepared. It sounds so simple, but it's not easy (but it shouldn't be hard either!) After all, you've done the hard work already. You've researched and written the thing. It's just a matter of defending what you have already done. That's in the past now, and you can't change it. But you can acknowledge that and understand that it was never going to be perfect, and it doesn't need to be.
So, my viva prep will consist of rereading my entire thesis (which I haven't done in two months), and acknowledging what the strengths and weakness are of each chapter, and each of my main arguments. I've already made a list of likely questions (the typical ones most people are asked, and ones specific to my research) and started to make bullet point answers to them. Once I've gone through all the chapters, I'll go back to those questions and have another go (and see if any more questions occur). After that (which I figure will take about 2 weeks), I'll have a brief look to see if (shockingly) anything new has been published on my subject since September last, and then have a look through my external's publications (again) to remind myself where they are coming from (those will take about a week). At that time I'm going to be getting on a place to return to England, so that's my deadline. It also means I'll get a bit of a break right before my viva, because it's hard to concentrate with jet lag!
As for the run-up to my viva, I've got stuff to do and places to be the few days before, so that's good distraction. And I've got an amazing supervisor who has offered to be there if I need help (
But, in the end, the best piece of advice I have ever been given is...enjoy it. It's probably the hardest piece of advice (considering I am A) prone to fists of anxiety and B) a worst-case scenario-ist). I do, however, aim to try.