It's been a while since I gave my A-Level exams but I remember the key was just practicing as much as you can (past papers). No I did not join any academy and frankly I would not recommend it at all. Just go to all your classes, read your assigned book/s whenever you can and when the time comes do as many past papers as you can and you will do just fine. I gave A level Math in a year so I don't really remember how the syllabus is divided. Best of luck.