Start writing essays early in the year. I personally started writing essays extra to SACs in the middle of Unit4, which was a big mistake. I also regret not touching my books during the summer holidays.
Now my main 3 tips that helped me to improve my writing from 3-4/10 to close to 9 and 10 at the end.
1. Look up basically every single word in a thesaurus and expand your vocab.
2. Get your essays marked by your teacher, but also upload them to the
English work submission and marking thread.
I personaly liked the AN feedback way more than my teachers feedback.
And more importantly rewrite your essays a few times as well, especially the ones that you write outsides of swotvac.
3. Also you may consider getting a tutor. I had an English tutor (werdna on AN) for the last 5 or 6 weeks iirc before the English exam and it helped a lot.
In essence, by starting to study for English (or ESL in my case) I learned to love the subject and in the end it was one of my favorite subjects, after methods.
English can be a really fun subject.
Good Luck Next year