Step One For Viva Prep: start.
“Do I start now? Am I doing the right thing?” Just begin. Wondering if you need to do something now or later? Do it now. There are lots of things that you can do which will help; find out what they are and do something to help yourself.
…all of that said…
Step Zero For Viva Prep: make a little plan.
It doesn’t have to be the most detailed thing ever. Figure out how much time you’ve got left. Think about what might help. Allocate tasks to certain days.
Then see Step One.