Yes you go through some good books or websites that teaches about the grammars. By going through the notes you can improve your grammar. You can read more and more books like stories, novels and all so that you can understand the exact way of using grammar. I was also very poor in grammars during my school and college days. I used to get low marks in the essay writings kind of tasks because of less knowledge on grammar. But I was trying hard to improve my grammar by going through the written work received, by communicating with friends, by going through books and all.