Refresh your memory: read your thesis, check a few papers and make whatever notes you need to feel confident that you know what you need to know.
Review your thesis: add annotations to create the best supporting resource possible for your viva.
Rehearse for the discussion: you have to be ready to talk.
Reflect on the journey: remember why you have got this far – not by being lucky, but by working hard and growing as a capable researcher.
Rest: give yourself space to breathe.