I am not sure I am the right person for this. I am not a native English speaker and I don’t work in education. What I do is online, not academic writing.
My advice is to ask someone who does such my fellow writers Trisha Traughber, Chris Ing, or some other native English teacher / literature student. It sure does help to read a lot of high-quality books. Also, try to get track of what your teacher minds most about your writing — vocabulary, structure, how you explain your point of view, etc.
I also had a high school teacher who would often give me bad marks (I couldn’t understand why) but it was a different thing at university.
Best od luck!