Remember to let go and be as calm and relaxed as you can at a test.
It seems to me that too often we try to hold in our conscious memory everything we learnt and everything we 'think' we need to know for the test (and in other areas of our lives). Then when we sit down to the first question we discover that it's not one of the answers that we are holding consciously it's probably one we need to access in our memory banks, we panic. This is were we start making silly mistakes.
The conscious mind can only hold 7 (plus or minus 2) bits of information at any moment. In order to access our memory banks it has to 'forget' some of that information. Once something just disappears from the conscious memory we think it's forgotten for good so we panic. We try to 'tighten our grip on our conscious memory. The tighter we hold onto the information in the less accessable our inner memory is to us. So we make silly mistakes and not only on tests. We need trust that we can call upon our inner memory and therefore let go of the answers we think we have to have.
The personal Genius and the Memory Supercharger paparlimials are great aids to developing that trust.
Remember also to work out quickly how much time you have for all the questions. Leave yourself a proportion of time to go back and finish any unanswered questions. E.g. you have 5 essay questions to be completed in 1 hour. Initial calculations mean that you have 12 minutes for each question, However if you allow yourself 9 minutes for each question you have (9x5=45 60-45=15). That leaves you 15 minutes to review and complete any questions. So you answer as much of each question as you can in the 9 minutes, once the 9 minutes are up you start the next question. If it isn't complete leave some space and go on to the next question. A partially completed question scores more than a completely unanswered on.
Use that technique on all your questions to avoid spending too much time with any one question. Leave yourself a bit of time for a quick review.
Read all the questions first and if you know the immediate answer fill them in. Then on a second pass fill in the slightly harder questions, because your mind has read them it has now had a chance to start working them out. Then repeat with the more difficult questions. Remember never to spend more than your allocated time with any question.
Alex