Usually schools have techniques for essay writing. my school uses PEEL - point, explain, example, link. there is also TEE which is technique, explain, effect.
also the HSC study day I went to, they said focus on concept, not context so don't get stuck into the storytelling (which is what I do oops), and focus more on in depth analysis.
basically, just keep writing and writing and you'll get better. write out like a few different introductions, a few different paragraphs for each paragraph, and basically keep writing essays and have friends or teachers check over them!
If your English teacher is not much helpful, then I'm sure there's plenty of English teachers at your school who are willing to help.
