Hi, (my comments relate to Australian PPL exam, not sure how relevant that is to you. but here goes...)
I recommend the Bob Tait PPL book. It has lots of sample questions in it, some of which are practically identical to some I had in my exam. I purchased a practice exam, which I would not bother to do again. The sample questions give you the gist of how questions are structured.
Be sure to know how to calculate start and end of daylight, and how to apply that to practical situations - for example a flight leaves Echuca at xxx for Alice Springs. How long have you got for the flight? Ensure you fully understand the terms used - "mean time", "local time", UTC etc.
Weight and balance will come up too, and dont forget to revise your BAK stuff.
Air law is important to know. You can find the answers in your reference material, but you should know the basics. I had questions on number of passengers, age of passengers, doing practice stalls with instructors.
Know how to find answers in your reference material. In OZ, we have a Visual Flight Rules guide which is very handy, but the index is hopeless and you need to know where things are, for example the conversions page or VFR minima for alternate. The VFG has some clanger mistakes in it too so know about that. (The OZ VFG 2007 has incorrect end of daylight graph and incorrect declared density chart - handy not)
There was a couple of questions on navigation and flight planning. They were pretty simple. Just a straightforward flight planning exercise with a deviation at some point.
If you'd like to know more, send me a PM, I'd be happy to elaborate further.
Cheers
Richo