Schedule meetings with your teachers to discuss your strengths and weaknesses. Make notes about how you can improve and what units of work you need to focus on.
Practice taking the tests online. Make sure that you start doing this after revising for a suitable length of time as a large part of practice tests is to do with building up your confidence; if you start taking these tests too early on, you may find that your score suffers and it will dent your confidence. Find these tests online (see the resources list below) and you can also buy the practice test books in most quality bookstores.
In the actual exam, plan your answers before writing your final response down. Think your ideas through and create a mind map to ensure that you give full, well-constructed answers. Writing a long answer can often lead to confused, unfocused responses so plan your answer first and tick off each bullet point as you cover it.
Read through your answers at the end of the exam. Check for mistakes and make sure your essays don't have any spelling or grammatical mistakes. Leave a suitable amount of time at the end of the exam to check your work without rushing.