Six of the 8
Manhattan GMAT Strategy Guides (all the math books, as well as Sentence Correction) have a division between Part 1 (General) and Part II (Advanced)
We suggest that you master the content covered in the General material before moving to Advanced material. That is, make sure you're completely comfortable with with the General reading, the General In Action problems, and the General OG problems (at least the Benchmark problems) before moving to the Advanced reading, In Actions and OG problems.
If, while going through the General material, you want do a little Advanced work here and there, that shouldn't be a problem. But it's important to first build a solid foundation in all eight subjects by mastering the General material before focusing on any Advanced work.
I hope this helps! Good luck with your GMAT studies.
Best,
Matt Mapplebeck
Student Services Associate
Manhattan GMAT