From a survey of all the 'A' level top scoring friends that I have, I have noticed a common advice they always issue: sleep at least 7hrs.
Here's a sample of how these guys have fared in their 'A' levels in 2005:
Anglo Chinese Junior College, 9 Distinctions, awarded the prestigious Medical PSC scholarship
Hwa Chong Institute, 9 Distinctions, A*Star scholarship
Victoria Junior College, 7 Distinctions, 2nd-tier Police Overseas Scholarship
For the record, students who score 9 distinctions in their A levels rank amongst the top 10 students in Singapore for that cohort. I had the privilege of meeting these outstanding scholars through my time in the army, as I was undergoing officer training.
The first student, Loh Wei Liang, made it into Medicine school in Singapore and was awarded the first ever PSC scholarship for medicine. He's a very friendly guy who played rugby in junior college. Was not much of a 'mugger' or somebody who studied extraordinarily hard. He enjoyed his rugby sessions and made a point to sleep at 10pm everyday.
The second student, Wu Sheng Rong, is currently studying Science in Cambridge university. He doesn't seem to have any problem there at all, applying the regular sleeping schedule that he kept in Singapore during his days in Junior College and in the army. He always appeared as a calm thinker to every coursemate, and even my course officer, Captain Clarence. As with the first student, Wei Liang, I was the room buddy to Sheng Rong as well. I had ample time to chat with them to slowly uncover the secret to their academic successes.
The third student, Zhi Yang, was a bunk mate from Basic Military Training Centre (Army, of course). He too strongly espouses adequate sleep over mentally drudging through a day in school.
These people slept, and still sleep at least 7hrs a day before their lessons the next day. This is so that they could concentrate thoroughly in class and acquire full understanding of the topic at the lesson. The full, uninterrupted rest obviously gave them the ability to focus so intensely in class.
As of myself, its a rather sad story. However much I mugged (studied my brains off) in JC, I could produce only 4 distinctions in my A levels. I noticed the very grave mistake I made in staying up till 2 or 3am everyday and dozing off in classes. Not a good strategy. If only I had the chance to learn from these successful scholars earlier.