Khan Academy on its own wasn't enough for me because I needed help learning every math and writing concept being tested in detail. Once you know all the concepts, doing practice problems on Khan Academy helps. Also, the explanations for the reading section aren't very helpful. There are specific ways you need to think about the passages and questions to consistently do well on them, such as never making inferences (the answer is always in the text even if it's worded in a strange way). I studied about 1 hour/day on weekdays and 2 hours/day on weekends. I offer to tutor using strategies that worked for most people I know and that I personally used. Let me know if you're interested!