Speak clearly, pronounce each word's ending so that it is understandable. Answer the question, do not go off on a tangent. Use details from the question material.
If you are truly stuck, say something even if its just ... "I can't understand this question." is better than nothing. If you just don't understand the question, say something which relates to the question. At least you will receive 10 points instead of 0.
Don't panic, practice with a native speaker whenever possible, and don't take the the test before you are ready.
Hope that helps.:)