Using the materials **by the company/people that administer the test** is a good idea. For TOEFL, for example, ETS partners with McGraw Hill to do the official test prep guide so you know it's based on the best information about what the test is testing for. Companies collect the feedback from candidates and teachers about what candidates have difficulty with, and so they deliver special activities/explanations to address those concerns. Use the materials designed by the people who research and iterate the test itself... I did a Japanese language exam a few years ago and everyone almost exclusively just studied the practice tests; the reading topics, the vocabulary, listening again and again to the listening sections. Sounds like you're on the right track with the online materials. G'luck..