I'll just give you general advice since I don't know what exactly you're struggling with.
My suggestion is to just do practice essays and continuously get feedback from your teacher(s). In order to succeed, you need to know what you're doing wrong, but also what you're doing right so you can keep building on the strengths you do have and start working on your weaknesses.
I used to get pretty average scores in English last year because I never sought help from my teacher, and any feedback I was given turned out to be pretty vague. That led to me not knowing what I had to work with, meaning that my essays would just consist of writing whatever came to mind without knowing which structures and analyses worked for the topic.
Since I started getting more feedback on my essays this year, my grades have been able to maintain a consistent high standard.
If you feel like you don't have the time to write whole essays to show your teacher, try writing single paragraphs and then working your way up. I recommend starting in an area you really struggle with, e.g. introductions, body paragraphs or conclusions, and then getting to your strong point.
This advice is pretty generic and I'm sure you've heard it many times, but I hope you found something helpful in what I said!
Good luck~