Firstly to go back through everything, watch all the free lectures on here, and make sure that you really do understand everything and are not just learning rules.
Secondly to practice and practice and practice. You must use a Revision/Exam Kit from one of the approved publishers (if you already have one then get one from another publisher so that you have different questions), and you must practice under time pressure.
It is one thing being able to get the answers correct, but it is another thing managing to get them correct under the time pressure of the exam.