Read the questions carefully. Understand what is being asked. Understand the length of answer demanded and the depth required.
Think of the answer. Plan the response. Judge if its the answer that the question is asking for?
Write the answer as planed. Stick to the plan, stick to the question and answer to the point.
Review the answer written. Re-read your answer and judge if that's the answer demanded by the question!
that's it. we all do this unconsciously in the examination hall, but this time do it consciously and see how it improves your exams.