Start your research early. While in early college, look online at a few PT schools that interest you and see what they have for prerequisites. PT schools usually have quite a few classes that they recommend you having before you apply, although some are not required.
Keep your GPA up during college. PT schools will admit students based upon a few factors, and GPA plays an important role in your acceptance. If you are above a 3.0, your chances are much higher in getting into PT school. Most PT schools require the GRE as a standard indicator of your education. Your GRE scores will also play an important role in your acceptance to PT school, so try to do as well as you can.
Do not neglect volunteer opportunities during college. Even if it is only for a few hours each weekend, see if you can volunteer at a local hospital in the PT department. Shadow a physical therapist for a few days/weeks and see what the career is actually like. In fact, some PT schools require a good deal of hours shadowing or volunteering with a physical therapist.