Resting
Include some rest time in your viva prep plan.
Your circumstances might not allow for proper time off. Holidays and breaks might be out but certainly give yourself time away from your research.
Your day-to-day life might be filled with work, family obligations or caring responsibilities. If this is so, don’t then go straight from submitting your thesis to viva prep.
Rest from your research. Rest from your thesis. A little breathing room will help when you return to your work.