for many people using the GMAT test books was helpful.
I would reccomend you use Manhattan GMAT books about the quantitative part of the test - in terms of general preparation
Another suggestion that I would give you is to really make the best out of the tests you do by
1) Re-analyzing them in deep, understanding the errors, categorizing the possible questions type and patterns - trust me it seems obvious but it is a huge effort to go back and look carefully - you can gain a lot from that if you really become "structured" about it
2) Maybe you already have explored - but just googling you find many resources that teach you basic strategies for the different type of questions of PST
Hope this helps.