Make sure you know which of the boards is setting the exam you will take, as well as the course work likely to be required. If taking classes, your teacher will be able to tell you. Each board's website contains vital information, as well as examples of past papers. The boards are Oxford Cambridge and RSA Examinations (OCR), Assessment and Qualifications Alliance, Council for the Curriculum, Examinations and Assessments, Edexcel and the Welsh Joint Education Committee. You are most likely to be dealing with one of the first three, with OCR the most popular.
Identify the requirements for the qualification. Passing an examination has always been an essential requirement, and the examination is likely to consist of two separate papers (prose and poetry). Increasing emphasis has been placed on coursework-written papers prepared outside the examination environment. The coursework is likely to include drama as well as more prose and poetry.
Know your texts thoroughly. There is no secret to this: it means reading the set novel or novels, the poems and the plays at least twice, and preferably several times. Preparing coursework allows you plenty of time to look up passages in the texts. For the examination, although you will be permitted to refer to a copy of the text, you will save much time if you already know it well. As part of your revision schedule, set aside time for a quick re-reading of the important texts as close to the examination as possible--for example, the day before.
Make notes when working through the texts for the first and second time. In the novels and plays, what is the motivation of the main characters? How does the author engage your interest? Are emotions or themes symbolized elsewhere than in the characters--by an animal, perhaps, an object, or even the scenery? You can use a notebook, of course, but also consider using index cards. You can use individual cards to make notes about characters or themes, sort them alphabetically and continue to add to them.
Seek help in understanding the texts. If you cannot grasp the main themes of a story or a poem, or the author's purpose, there are many resources to help you. If your teacher cannot answer your questions, visit a library and look up the difficult work in books about the author. Easier than that is to search online for summaries, notes and support materials on just about any set text.
Practice answering questions. If your teacher does not provide you with examples of past papers, find them online, at the boards' own websites or elsewhere. Answering practice papers against the clock will give you confidence for the real examination.