SAT Writing: How to prepare

Right now, I’m at a 650-700 for writing. I can’t seem to improve my score because on every test, there seems to be many new grammar rules that I have not learned. Do you guys know any grammar books that go into detail about grammar rules? How did you guys improve your score to 750 and above?

Hi! I got 770.

Erica Meltzer’s grammar book. It has most if not everything you need for the MCQ section.