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?
If you love reading or hearing at audiobooks I would recommend you to read/listen all Harry Potter books/audiobooks.
When I was learning English, it helped me a lot to hear Potter's audiobooks for enhancing my vocabulary and grammar.