Honestly, just harass your teacher with practice essays or if they get annoyed, maybe find someone (maybe a tutor?) who will be able to regularly review your work and give you really good feedback. Then use that feedback while writing other things to AVOID doing those again. Look at other people who have done really well and see how they articulate their words. Make sure when you read your essay it is EASY to read like it flows. You can't really study exactly for english except practising unseen comprehension for section 1 of AOS so you just need to refine your work constantly e.g. essays, creative, paragraphs, anything really