Well, I would suggest doing some sample tests from previous papers. Even if you have advanced English skills, you should get familiar with the test format. This will make sure you will know exactly what to do and how to answer a question when you see it and you won't get any surprises.
If you are weak in any skill such as writing or listening, I would then suggest working on those areas. I think it is logical that the more you practice, the greater the chance you will have at getting the score you want. Good luck!