The simple answer is that you need qualifications. So when you choose a school - and particularly a boarding school - you should consider its educational merits to judge how well you think you'll do academically there. Of course, to get into the more academically successful schools, you will have to sit a barrage of entrance papers. Yet once you've passed this stage, it will be up to the teachers at the school to help you get along.
At London's Winchester College, students tend to do rather well academically, even though the school focuses more on nurturing a love of learning than drilling students for exams. In my house year alone, three out of the 12 members of a group achieved straight A*s at IGCSE level, me included. At other local schools like Westminster and St Paul's, the story is much the same. The reason for this is both the quality of the students and the skill of the teachers.
Here are two bits of advice that I would suggest you take to heart: 1) Do pay attention during lessons. Doing so will make any work outside of class all that much easier. 2) Cram as much as you can in the holidays leading up to your exams. Don't waste your precious time playing Call of Duty: Modern Warfare 3 on your PS3 or XBox 360.
The Hong Kong way to ace exams is to hire a tutor to guide your every move. I think, though, that on many occasions, it's better to do the work yourself. That way you can truly absorb what you have learned.
Tutors should be there just to explain things and clear up any misunderstandings. After all, at times you may well need a qualified expert to guide you through tricky parts of a lesson.
Success at school gets you into university, and success at university sets you up for life. So choose wisely. Your life depends on it.