There are roughly a dozen topics in the IELTS exam. Any of these can be covered in your writing, speaking, listening and to an extent, reading exam.
That's why it is really important to know a specific set of vocabulary for each IELTS topic.
I have put together a succinct guide for topic-specific language for the vast majority of the IELTS subject matters.
You know how important it is to have a high level and range of vocabulary for the exam, but we need to be realistic. Learning new words aimlessly is not something I recommend. Because, how do you know where to begin, and where to end?
The solution I believe, is to learn words that are specifically related to the IELTS topics. In the resource I have created, there are roughly 15 words per topic, including synonyms, subject related words and collocations (signalled with a (c) next to the word), to help boost your application of language.
The aim here to cast a smaller more effective net, rather than a wider more aimless net.