Oral exams can be daunting because you are never quite sure what will come up and you have to think on the spot. There are many ways you can prepare, however. There will be subjects in the curriculum that will be covered, such as school, hobbies, travel, etc. I would start by jotting down some answers to questions you would imagine they could ask and making sure you have enough vocab in your word bank to be able to improvise. The more natural you sound, the better! I would also try to make sure you master a variety of tenses to show the examiner your knowledge - more complex tenses such as the subjunctive or the conditional will get you the higher marks. I would also recommend immersing yourself in Italian by watching films or listening to the radio. This will tune your ear into the sound of Italian and will really get you in the zone. It will also help you to work on your pronunciation, which is also something examiners look for in oral exams.