In the writing, were you trying to write from experience or just making it up? I find it harder to make the story from my own experience, or express my own views (especially if I don't have a view on a subject) so I made it all up, and gave views of others I've heard talking or at work.... who cares, all IELTS want to know is you can write well in English.
I don't mean to criticise, but you don't use many commas, which is where I would say you may be lacking. Your spelling appears to be fine so no problem there. I can't really talk about the commas too much, as my written English isn't all that great.
A great book I used is called Common mistakes at IELTS Advanced ...and how to avoid them, by Julie Moore. It's not expensive and available on Amazon. It's not one I'm going to sell, as it's that good. I also used the official IELTS material too, but they only show bad examples written by foreign students. They do have a model answer on some of the tasks though. It's not just about grammar and spelling, but answering the question and not veering off the subject.