Mostly students who appear in IELTS do not know about brainstorming. It is a pre-writing process in which you think about the given topic and put down on the paper as a mind map. It will help you that how would you write and proceed.
Whether you are writing for IELTS Academic or IELTS General Training, in order to make your ideas balanced and composed on the paper, you must think for at least 10 minutes. Make a map or a tree like this.
A Mind Map. Source: https://owl.english.purdue.edu
Put your essay topic in the middle, just in a single word and than grow it as much as you can in the specified time. You can make your map on the question booklet easily.
So start your practice of making mind maps on different essay topics.