'Distill' down the information that you need to memorise to it's basic simple facts and learn those, nothing else. Do not try to read around the subject or remember anything else. If you go into the exam knowing the 'bare bones' of your subject you will get your marks and pass.
If you have a good short term memory and you have done some work through the year you can also crash revise a subject the night before the exam. Revise the subject from 8pm - 1am and then get up again at 7am on the morning of the exam and do 2 hours of further learning. The info should then be in your short term memory (if it's up to it)
