One of the only ways to improve essays is to write alot of them unfortunately, so do lots of practise essays and get feedback from your teacher. The more you write the better you get at fluency and spelling, it is also a good idea to vary how you start sentences and how you use analytical language (if it's an analytical essay). Before you start writing, try planning each of the body paragraphs out so you know exactly what you want to write and how you want to write it.
Hope this helps 😄
