When it comes to oral exams it is easy to get nervous. However, there is really no need!
The most important thing to remember is to relax and be yourself. The aim is to have as natural a conversation as possible with the examiner.
I would recommend learning a few set colloquial phrases which you can sprinkle throughout the conversation - this allows you to show off all of the brilliant vocabulary you have learnt throughout the year! You may also want to think of some potential questions or themes which are likely to arise throughout the conversation. For example, if you have been learning about Spanish food you should learn vocabulary related to food. Flash cards help me to learn vocabulary! I use lots of colour and sometimes even draw pictures! You could also make use of online resources like Quizlet.