I can’t say it is the best way, but I used this approach and made major improvements in all my weak areas. First, know your weak areas. If you don’t already have scores, have someone administer a full practice test as close to real conditions as possible. Let’s say for example you find Math is your weak area…
Spend a week studying a prep guide (book, on-line, etc.). At the end of the week, have some administer a practice test for that area. Again, the conditions should be as real as possible. Set the timer and complete as best as possible. If you cannot complete during the time, mark the question you’re on and proceed to complete the entire test. Note the extra time needed. Correct all your answers. For every one you got wrong, make this the focus of your next study cycle. Repeat this sequence as long as possible until you have the results you are looking for.
In addition to the above, you should probably plan on taking at least four full / timed tests to give you practice for the actual conditions and monitor your weaknesses.
Bottom Line – aside from following the guide books, test prep offerings, etc. – I would strongly suggest that you ensure you have taken as many practice tests in your weak areas and full test as much as possible. There is no way to correct your errors unless you find them and dedicate time to remediation. If you perform well for the practice, you will likely perform well on the actual.
Good luck.