Make sure your essay is readable. If your essay is easy to read, you can get better marks. The IELTS exam marks for the second writing test are divided into 3 categories:
First, answering the question accurately.
Second, cohesion and coherence.
Third, language appropriateness (grammar, spelling, register etc.). When you see this you understand the importance of spending time thinking about the meaning of the question(answering the question accurately) and organizing your ideas(coherence) before starting to write. Work on these aspects of writing dramatically improves the quality of an answer without even beginning to look at grammar, spelling and register. Therefore, you must keep your ideas simple as this will help with expressing and organizing what you want to say clearly.