If you're doing it with WJEC then you'll pick two pieces of paper at random from a selection of around 8-10. One of these sheets of paper will have two pictures, and the other will have two short paragraphs. Each bit of paper will have 3 questions on - the first two questions are usually quite straightforward and can only really be answered one way. The third question will relate to the topic that the pictures/paragraphs are based on, (e.g. health/sport/freetime) and will also allow the examiner to ask you extra questions and start a discussion. You get 20-25 minutes to prepare your answers to these questions.
After completing the oral cards, you'll then have a 10 minute conversation about yourself, what you're studying, what you like to do in your free time, simple things like that. The second half is literally just talking about yourself - the only difficult part is that you might get asked a question that you don't understand, in which case, ALWAYS ask what the examiner means. You score well for keeping the conversation going, not just being accurate and knowing extensive vocab. When in doubt, stick in a "Wie heisst das/Was bedeutet das auf Englisch?" or something similar.
You can always lie in the second part obviously, but beware that the examiner will take the conversation wherever you want it to go. So for example, if the examiner asks what you do in your freetime, and you say you like dancing, then you can bet s/he will ask you questions about dancing and why you like it. If you don't know any German vocab related to dancing, then say that you like to do something that you can talk about.
Any more questions, feel free to ask. Or ask the OP, I feel bad for hijacking their AMA.