In trying to deal with this subject, consider the following questions. Why do we have nerves? What are nerves? And how can we manage them?
There are many reasons some people suffer more with nerves than others. When I think about nervous situations, most of the time they are there due to a level of expectation regarding the situation.
For example, the penalty kicks at a football match. The job of kicking a ball into a fairly large space seems straight forward enough even with a goal keeper in the way. Imagine this situation for the last game in a football season and both teams are mid way in their league and the outcome of the match makes no difference to the overall position of the teams. There is no pressure on the penalty taker and just pride to be lost if the goal is not scored. However, imagine both teams are at the bottom of their division and the outcome of the match determines which of the two teams are demoted. Straight away, the act of scoring a penalty has more significance and the task of actually scoring is immediately harder. Or is it? It is the level of expectation that makes it harder. The goal is no different to the earlier situation. The very significance of the occasion has created a nervous situation.
Another example, if the penalty taker has no experience of taking penalties, we have a different situation. Because of the lack of preparation, there is doubt and fear which are two very negative feelings that may distract the penalty taker. As before, the goal is the same but because of the situation, the goal keeper seems bigger and the goal smaller.
Regarding exams, the easiest way to deal with nerves is to lower or have more realistic expectations. For example, I have had many pupils when entered for exams say ‘I’m going for a distinction’. The level of expectation though admirable is sometimes a little ambitious. Any thing less than a distinction will result in disappointment so a pass which should be something to celebrate will be interpreted as failure. Another negative situation that frequently occurs is a pupil can concentrate so much on what may happen if they fail that before they go into the exam room, they have already convinced themselves of failing the exam.
Looking at the examples you may already have found strategies to manage nerves. Nerves can bring out the best in some and be destructive for others. Being familiar with the routine of a situation will make the experience more enjoyable. It is a good idea to talk through the procedure of an exam with the pupil so they are aware of the format an exam takes. I have heard of very capable pupils preparing for an exam only to leave the exam room distraught because they were unaware of the format the supporting test Aural takes.
If there are weaknesses with the exam for example, scales and arpeggios or one of the pieces, then dealing with nerves is a little harder. Try not to focus on the weaknesses. Your teacher should be aware of these and would have evaluated whether an option could be to withdraw from the exam or consider taking it at a later date. If the option to continue is taken then there is a chance that the situation is not as bad as it seems. Messing up a scale or even scales will not necessarily mean that you will fail the exam. Gains can be made on other aspects of the exam for example Aural or a stunning performance of one of the pieces of music or the sight reading.
We all suffer with nerves from time to time. Keeping realistic goals will help to minimise the effect that nerves have on a performance or exam.