This is the style I followed. Remember for me even basic grammar was a problem.
1. Learn the basic grammar from some good books like wren and martin
2. Graduate to Manhattan SC book available free on the net.
3. Test whatever you have learnt using the 1000 SC docs. Acutally there is a free website that lets you test your SC skills
https://www.gmat-success.com/gmat-sentence.html. Now this site is primitive compared to questions asked on the real GMAT but then for me this in itself was a graduation.
4. As you reach abt 70% on the SC, search for 800Bob's posts on testmagic forum for SC. Every post is crystal clear and this will help you in further understanding the patterns of SC.
5. From here on you will be in the 85-90% range and you will be able to solve questions in the forum. Please avoid solving any GMATPrep questions in the forum at this stage.
6. Take the Powerprep tests and see where you are. If you need more practice, 1000 SC is the place to go.
7. Now take the first GMATPrep test.
8. Book your test date based on your comfort level and score.
9. From here on keep taking GMATPRep test I as many times as possible till all the questions repeat.
10. A week before the test take GMATPrep II. After the test solve only GMATPrep questions on the forums.
Follow the same strategy for CR and math. Now RC is a different beast. You have to consistently read "Good" boring articles on the net. Also remember that your expertise in CR only will help you solve tough questions in RC.
Hope this helps