Many of my students talk about motivation, but discipline can be more powerful.
In the IELTS exam, you will be docked points for wrong spelling. While most students spend a lot of time learning vocabulary, or understanding how the exam works, they often forget to learn how to spell.
Mistakes are an accident. You know it's wrong, but the wrong word slips out. An error, on the other hand, is something you don't know. But what's the difference when you study?
There is a good chance that you have written a lot in English but you still find that writing is frustratingly slow. You have been practicing, but the bottleneck issue could be that the way you practice reinforces your bad habits.