Some students recommend answering the 'known' questions first. That way, they pick up the easy marks before tackling the toughies. However, when doing so, cross out or clearly identify those already answered and circle those being deferred on the exam booklet. Then, you can easily go back to them later. Also, sometimes hints from later questions may spark your memory and help answer those that you are having trouble with. Further, nervous types tend to calm down when working their way through an exam. A question that seemed confusing at first, may be much clearer later on.