Alright! I have got some tips for all those GCSE guys who would appearing for the first time for their exams.
#1- Keep calm and composed. Don't be nervous! No matter what, don't stress.
#2- Take breakfast the morning of yoru exam day. Even if you don't want it, your blood sugar level should be high enough to keep you get working until it's over.
#3- Drink a lot of water before exam, I don't mean immediately before exam, or you would have to use the restroom every now and then, which isn't a good idea in exam. I mean like an hour before, keep yourself hydrated. This will keep your mind and body fresh.
#4- Sleep well. I know how it feels like, like you have to revise this and this, then will go to sleep. But BELIEVE Me! Whatever you read in the last moments, you are not going to remember a word of it!
Relax your mind before exam, don't even think about anything about exam! Pretend like it's a very normal day. When you do that, your mind would give it's best in the hours you need it the most!