The International English Language Testing System (IELTS) exam is taken to measure a person's English proficiency. I wish schools could have trained students for these type of exams and did mock tests. There is actually a good learning structure as foundation in writing a good essay. I wish I had that knowledge earlier.
In order to get your desired scores, I suggest to enroll in a review center that does one-on-one coaching. If you prefer to self-study, however, that can work too as there are several resources online that I found useful.