I will be taking the GRE test, which is an exam for students from non-English speaking countries who want to go to the US for graduate study. The test basically tests your English ability and your logic (math) and critical thinking (in writing), and I have a half year to prepare for this.
I don't know is would be appropriate to read books like "Ways to improve your English Writing", or to just read as much as you can. Someone thinks Russell's "The History of Western Philosophy" would be helpful for this exam - and indeed it is good - but I just think it's a bit hard and I might not have much time for it before the exam.
How can I study to improve my writing in these areas? Should I read books, or is there some other way I can improve? Is this a writing problem? How can I prioritize my learning?