For my biology exam i had 2 weeks to basically learn the biology spec because our teacher wasn't in school for 3/4 of the year. What i did was open up the spec for your exam board and go though the revision guide along with the spec, so look at the spec on the first topic and then open the revison guide and learn the facts that you see by heart. 1 read it 2 try to say it to yourself do this a couple more times, continue this for every topic. Once you get in the groove youll be fine. Also the night before try and do 2 practise papers to get the exam knowledge. When u are cramming i feel that it its important to at least one paper before the exam just to get in the test mood. Other than that, good luck and dont bother writing notes or revision card just hardcore memorisation and you will be fine.