Go to the Review page and use the filters to identify which question types/subjects you typically have the lowest "percent correct" or slowest pace, and work on reviewing those particular question types/subjects. If you've exhausted all of the relevant lesson videos and practice questions in Magoosh, you can find some extra tips on very specific kinds of questions by digging through our blog posts (let us know if you need help finding anything!): http://magoosh.com/gre.
In addition to this, go over your old questions-- not just the ones you got correct, but also the ones you got incorrect. You should be able to explain to yourself not only why the correct answer is correct, but why the incorrect ones must be incorrect. If you get stuck on anything, definitely feel free to let us know and we can walk you through it :)