some things that really really help: once in a while take untimed tests and see how you do. This will help you determine your actual best possible score. Also, when you are taking tests, mark each question that you think is really difficult and whether you get it right or not go back over them and see why you got them right or wrong.
I agree with the untimed test advice. This is the only way you can determine if your brain is not getting enough time to thoroughly process the information or if you truly don't have an accurate idea of what the questions are looking for. I think this may be a good step in your preparation. Good luck!