How do I ace my PSATs ?

First of all, I have been studying for my PSATs since 6th grade.( I am in 8th grade now) I am doing 3 years ahead in math and I'm doing advanced language. I think I can easily get 800 in math , but I am not so sure about critical reading and writing. I read alot but how can I spread my vocabulary and improve my grammer? If I take the PSAT right now I think I will get like 800, 760, and 740.