Failure to answer the question can cost you marks. You must work out exactly what the question is asking and make sure everything you write is in answer to the question.
Of Mice and Men
You need a plan before you start writing to check you have included all you know, to make sure you are answering the question and to time your answer.
Work out how long you have to answer each section in your plan, leaving 3–4 minutes at the end to check your answer. Don't rely on that alone though. Make sure you read back over each paragraph as you go along.
It's possible you may have made mistakes, and if you do not read through to correct them you will lose marks unnecessarily.
Remember to keep calm and try to concentrate on the question.