Not to sound like a broken record...but practice, practice, practice.
I took my PAT from a 19 last year (very little practice) to a 28 this year (whole lotta practice).
I used the following materials:
-Kaplan blue book and the full Kaplan course. I wasn't a big fan of shelling out boku $ for Kaplan, but I must admit, all of the online material (workshops, practice tests, etc.) helped me out a TON.
-Barron's, which has a good PAT section.
-DAT Achiever, which has ridiculously hard PAT sections.
Regardless of what you use, practice, practice, practice.
Good luck.
Brian