Hi Markov, it is a scary time, I remember it well. To prepare, I re-read my thesis and all the key papers I had referenced. I also read my examiners’ papers to get an idea of their approach to the field. I think having a mock viva (with your supervisory team) is invaluable. Above all, be confident in your viva (even if you don’t feel it!) but not arrogant. Remember that no thesis is perfect and if you are aware of flaws or shortcomings (and hence, prepared to defend them) you will be ok. Best of luck!