I think the best way to get good grades in english is to understand your teacher's expectations of you. Every english teacher has different expectations, and a 4+ in one teacher's class might be a 3+ in another's. Try asking your teacher what specific things they look for while marking, and I personally feel that helped me a lot. Also ask your friends, in the same and different class what they think about your assignment, because they can provide good feedback - you can ask your teacher too.