You can actually start straight preparing for PST and similar tests to stay focused on your main goal and get really well prepared. There are plenty of guides and free exams on the internet that you could take as a real example. Here are some tips that will help you to prepare for the test in whole:
1. Carefully select and make a list of your practice material.
2. Practice quick math.
3. Improve your data analyzing skills.
4. Learn how to speed-read.
5. Practice under real stress conditions (limited time).
Wish you luck in the test passing!