Relax! : Although you feel nervous, you have to pretend to be relaxed and confident. The teacher wants to see a student who is able to speak and communicate something rather than a student who is a bundle of nerves. It may be difficult but in an oral exam you must keep your wits about you. It is one of the most important things. 

Be natural, fluent and spontaneous. For a teacher it is more important that the student knows how to communicate a message than the fact that he/she makes grammar mistakes. Show that you are able to communicate and speak fluently. To do an oral exam it is good to know some recurrent sentences  you can always use

MONOLOGUE : If you have to speak about a topic: 

---Always introduce yourself:  

Good morning, my name is ........ I am studying English in Valencia. I am a teacher/student... Tell the teacher a little bit about yourself.

---If you are asked to talk about a given topic, always emphasize the relevance of this topic. For example, if you have to speak about new technologies, say something like this: 

Nowadays new technologies are very important . We always make use of them. More and more, teenagers use mobile phones everywhere and for everything..... (the importance of this topic in today's society) 

--Then, if it is possible,  mention advantages and disadvantages. There are advantages like... However... 

Give your opinion and tell something about your life. In my opinion, the use of new technologies is not always positive because... For example, when we were younger...  

-- Finish the monologue in a polite way : Thank you very much for your attention 

Interaction  

The teacher evaluates your interaction, so let your partner speak as well. Don't be selfish! 

A dialogue is a conversation, so use sentences to interact such as: Do you agree with this?/ I don't agree with your opinion/ I am afraid I can't do that/ what do you think about...?/ What about that? Make sure the communication is flowing. 

The dialogues have to finish with a final decision. Most of the tasks are about deciding something with your partner. Therefore, the teacher is waiting for that final decision. Use sentences such as So, what should we do?/  I think we could do.../  Let's make a decision because.. 

If your partner says : Let's meet at 4:00 pm. Don't say yes. Try to speak more:  I'm afraid I can't because I have an appointment with my doctor.. Try to develop your answer and avoidyes/no answers. 

REMEMBER

Smile, greet the teacher,  be confident and speak. Silences and long pauses are dangerous. If you don't understand what the teacher says, don't be afraid to ask. Sorry, can you repeat? Sorry, I didn't understand  There is nothing wrong in correcting the mistakes you make