First of all, congrats on the invitation and best of luck in the process. A few of my friends have had experience with the PST and I'd be happy to share a brief overview of their suggestions / best practices.
In short, since the PST tests business acumen along with math abilities, it is important to practice both of these areas. The main difficulty with these tests happens to be the fact that you will not have enough time to comfortably answer each question. Therefore, it is important to be agile and precise.
In terms of tips and tricks, I would suggest the following websites (see below) to go through some sample questions. At the same time, it is always great to work on your mental math (PrepLounge offers some good resources for this). *Note: I've included GMAT and GRE questions because these are challenging and, in some ways, reflect the mental process you'll need to solve the PST math problems.*
If there is anything else you need help on, please feel free to reach out.