English grammar

I have a written test for interview in coming days. In the written test, Verbal ability has most portion of syllabus. I am not a native speaker nor expert in English. I am just beginner in English, but I have to clear written test for my dream job. So I need to improve my Verbal ability. So can anyone help me how to improve my verbal ability? I mean which books should I follow?

Thanks in advance.
I think you already figure out my English written skills after reading my post. So please me guys.