The biggest mistake candidates make while preparing for IELTS is that they prepare on their language skills alone ignoring the more important aspect, communication. To understand it, we need to differentiate language from communication.
Language to communication is like what buses and cars are to transportation. Transportation is movement of people and objects from one place to another for a purpose. Even if you have a nice car, if you don’t know how and where to go, it has no purpose. Just like this, even if you have lots of vocabulary and grammatical skills, if you don’t know what to say and how to deliver, your language is not functioning. This is like a person with an old bicycle with a plan of travel and the knowledge of the road can reach the destination more efficiently than a person with a Lamborghini with no plan or roadmap to his destination.
The importance of communication for IELTS is clear from the score descriptors of each module that, half of the score is derived from a candidate’s communication skills. In speaking, Fluency and cohesion and Pronunciation are communication skills but Lexical Resource and Grammatical Range and Accuracy are purely language skills. Same as this in the Writing module, Task Achievement or Response and Coherence and Cohesion are the determiners for half of your score. So It is very important to understand that you need to practice both on your language and communication skills.