How to study well English grammar?
My advice is to learn English grammar through books. You should read children's books and English books. If not, then you should buy bilingual funny books to read both entertainment and remember the grammar structure used inside. From there, learn, take notes to apply when needed.
And, what is your advice?
All of that is a waste of time if you already don't know the basics. If you know something then you can use books and learn grammar but if you're a total newbie then the best way to learn some language is to hire a tutor or sign for a language course.