Studying grammar will only slow you down and confuse you. You will think about the rules when creating sentences instead of naturally saying a sentence like a native. Remember that only a small fraction of English speakers know more than 20% of all the grammar rules. Many ESL students know more grammar than native speakers. I can confidently say this with experience. I am a native English speaker, majored in English Literature, and have been teaching English for more than 10 years. However, many of my students know more details about English grammar than I do. I can easily look up the definition and apply it, but I don't know it off the top of my head.