I did the same thing CTIIpilot did. I printed out the Delta study guide, and filled in the blanks with the ATP guide and other resources. I focused specifically on aerodynamics, weather (know about isobars and all about fronts), jet engines (especially where the air has the highest/lowest pressure), and pilot math (fuel dump/descent rates). I also reviewed the questions of WFFF. All the people I have talked to who used prep services are glad that they did it. Like I said, I used the ATP study guide, but excluded anything that had to do with running charts or computing CG (that doesnt include what changes in CG does to the performance of a jet). The test is really basic. Review your stuff, and youll do well.