I got 5 9s 5 8s and an A*
My biggest advice is to not stress your self out about getting all 9s and to actually enjoy yourself and take care of your mental health.
For me, stressing out probably had quite a negative affect on my grades. On the nights before a couple of my exams I couldn't sleep because I was stressed out about them which probably caused me to get lower marks than I should have. I have friends who flunked their exams due to them panicking too much during the exam and not being able to concentrate. Telling you all this might stress you out even more but my point is this : you need to be stressed out the right amount. You need to be stressed enough so that you actually revised but not so stressed to the point where it negatively affects your performance.
Imo, targeting yourself to get all 9s is going to put you under too much pressure in the long run. There is no practical reason to get all 9s at all. Yes you should do as well as possible but there is no reason to get all 9s. There are people who got into Oxbridge who didn't even pass all their gcses and there are people who got all A*s and were rejected. It really isn't that relevant and once you start your a levels you will realise how irrelevant they really are.
Okay so now I will tell you how to avoid stress:
1) Start revision early - This will help you to be less stressed. The later you start revising. the more you are essentially cramming the knowledge and the more stressful it will be. I didn't revise for RE until the day before the exam and let me tell you it was stressful lol. Don't be me.
2) Revise in an enjoyable way - My method of revision was to just read the revision guide again and again which as you can imagine was very boring. This resulted in me being very depressed and doing less revision than I should have done. I would advise you find a way that you actually enjoy. Making posters is technically less efficient but if you enjoy it then you will end up doing more revision in the long run.
3) Still have fun - so many people become anti social and shut themselves up in their rooms around exam season. This is definitely not what you should do. You should still take part in hobbies and get regular exercise during exams. Reward your hard work with something you enjoy whether that be going for a walk or watching an episode of a series on Netflix lol this will help you enormously. Still go and see friends and try not to talk about exams with them. Remember that there is a whole world out there outside of exams.
I hope this helps. I'm not trying to be critical when I say you shouldn't aim for all 9s. There's nothing wrong with being ambitious but I just think that having such high targets will do more harm than good. Although it's your call but just make sure you take care of your mental health and realise that GCSEs aren't everything.