A common grammatical mistake I see is when people use It, This and That in their writing. These words are important because they are used to refer back to something mentioned earlier. Referencing, or referring back in this way, has an impact on your Coherence and cohesion score. The image below shows how to use It, This and That correctly, so that you can explain your ideas clearly in IELTS writing.
You can find out more about clearly explaining your ideas and improving your Coherence and cohesion score in my interactive course: The Key to IELTS Writing Task 2.