Good luck for A's guys, the worst will be over very soon!!
There are TWO keys in winning the A levels:
1) Consistence.
If you HAVE been consistent in your studying by managing your studies, play and other commitments well enough, congrats. You're ready to attempt the papers.
Forsake your usual playing time and convert them into study time though. Now is too crucial a time to play, because every. second. counts. badly. A extra minute would probably add in a extra nugget of information and that could help you.
Of course, there is nothing wrong in taking a SHORT break every hour to help relieve the stress. But make sure you don't end up studying 30 minutes and playing an hour. If you end up in THAT stage, it means you're probably better off resting for the day.
And please, do get enough sleep (8 hours recommendation) and water and consume your meals properly.
A problem with many students (especially when it comes to exams) is that they do a excess of snacking and skipping of proper meals. This, isn't healthy eating, and the last thing you want to do is to fall ill. So consume proper meals (something healthy would help) and cut down on all the non-healthy food.
A bit of exercise during this period would also be beneficial. Go for a run if needed be - it relieves stress and allows your body to do some working out.
2) Confidence
Don't go into the exam hall panicking; if not you're on the losing side of the battle. Go in with the confidence that says "I will win this!" and with a smile on your face. It'll lift your morale, which would allow you to answer the questions better and give you a clearer mind to think properly, thus answering the question better.
Of course, it also scares other people, by making them thing: "Wah lau! This guy is walking in with such a smile, must be all ready to score sia! Die! I'm not ready!"
Of course, don't be overconfident and cocky, because it'll burst your egos and make you panic even more
All the best guys and girls!! Good luck and God bless!