I know it's easy to say when I'm not doing them, but it's always good to take care of yourself during exams.
This year, I did A level physics which was three exams over the course of two weeks and I found that tiring. Most A level candidates are doing triple that and GCSE candidates get about 20 exams in 5 weeks!
The most important thing is to get enough sleep. You might feel like you need to revise more, and maybe you do, but if you don't get enough sleep, your revision will not be effective anyway. You may feel that you haven't done enough the night before the exam, but by that stage, your choices are to have a good night's sleep and not be ready or to stay up all night, feel exhausted and not be ready. You should at least take the night's sleep.
Next is food. I'm terrible with food under stress - I eat all kinds of junk. Some people don't eat. It's best to eat something healthy - make sure there is healthy food in the house and that you get reminded to eat enough/not too much.
Next is something to do to "reset" your brain. If you do revision all of the time, nothing will go in. Sometimes, revising another subject helps, but sometimes, you've had enough. You need something to do for a short amount of time that will get you back on track - a game, a run, some other form of exercise - and then you can go back to the revision with fresh eyes.
Also, you might want to think about screens - phones too distracting? MAybe you could get an app that prevents you using other apps for a fixed amount of time, otherwise you might fall down a YouTube black hole and before you know it, you've spent an hour watching cat videos.