My suggestion is don't read the question paper at the begining.Solve what's in front of you. If you read the question paper at the begining you'll start thinking about other questions rather than focussing on what's at front of you. Within a min or so you'll know whether you can solve it. If so complete it or else just move on. If your not able to solve a problem just forget it. Remember that 80% is a really good perfomance. Make sure you mark the question, the answer of which you want to double check. And complete the paper half an hour before so that you can go through the whole paper again. Give more importance to the question that you've marked. All the best.. And remember a calm mind is a more efficient mind, :-)