Depending on the exam board, your speaking test could include many different elements - presentations, questions on a topic, general conversation, roleplay, even interpreting. It might be with a teacher or a visiting examiner. It might be marked on the spot, or it might be sent away.
Whatever format your exam takes, you can still find plenty of good tips to support you.
Know what you actually have to do. Do you know the answer to the following questions?
When is the exam? Orals are usually before study leave and the rest of A-Levels but the dates are often chosen by your school. (This may not seem important but if you've got other exams such as art or music practicals, or even another language, or you've got commitments such as University open days, for example, then you need to sort something out).