Study, Study, Study!
You'll be getting a very extensive packet in the mail, study every bit of it cover to cover. Know the PA32 white sheets and POH cold, especially if you have little/no PA time. You'll also be getting a GPS simulator program on CD, or if you want to get a head start you can download it at garmin.com . We have the GX50 in every single aircraft we fly. Spend a solid 4-5 hours with it, especially if you don't have a lot of GPS experience. A third to half of the approaches you'll do in training are GPS approaches. Go over chapter 5 of the AIM once and the section on GPS. Do not worry about Part 135, we cover the GOM (the parts of 135 we use)extensively in class. Have Fun!