Reading books, novels, and magazines will help a lot in
improving your grammar. It's a nice thing to do because aside
from enjoying, you also get to learn. Also, watching youtube
videos is great. These stuff are what my youngest brother (at
only 9 yrs of age) have done to be very fluent in english since
they do not have it yet in their curriculum. These are also my
hobbies so I suggest you try it too.