I got definite As in Biology, Maths, Psychology and Philosophy and a possible A in English (please let the remark be good pleasepleaseplease) and I just made sure I understood everything in class and had my notes up-to-date. I started doing a few past papers around April time and in the couple weeks before the exams up to the evening before, packed in as many past papers as possible and studied the markschemes/examiner reports. With essay subjects, it's about nailing that exam technique as soon as you can.