Paulo from Italy wrote and asked which grammar book I recommend. My favorite advanced book is “Understanding and Using English Grammar.” by Azar. When I taught at Santa Monica College I often had students buy that book. I love it. I have never found a better grammar book in all my years of teaching.
Go through all of the exercises in it. Make sure you know all the rules. It’s a good review for those of you who have been out of school for a while.
As I said in a previous post, people will sometimes think they hear an accent when you are making grammar mistakes. Something about your speech will sound foreign to them.