We know from the public version of the IELTS Speaking Band Descriptors that your use of vocabulary is one quarter of your score.
We also know that …
Source: the public version of the IELTS Speaking Band Descriptors
The public version of the IELTS Writing Band Descriptors make a similar point.
We also know from the ‘Idiomatic Vocabulary’ section that idiomatic vocabulary can also be rewarded – but idiomatic vocabulary is difficult to integrate into writing, and to be effective when speaking, needs to be given with natural features of pronunciation – which is even more difficult for the learner.
So, let us here just focus on ‘less common’ words. An IELTS 7 user of English begins to use them, and shows an ‘awareness of style’ and ‘collocation’ ( = putting two words together in the correct way).
Notice that the words are given one at a time, with full explanations, other forms of the word, and example sentences. Play with the words one at a time, explore the meaning, check it also in your dictionary, and write it in your vocabulary notebook with an example sentence [Reading Strategy #6]. Remember, simply studying a list of words is a BAD strategy [Check: Tricks Bad School Use #3].
So, develop your vocabulary day by day by checking out the pages in this section. Try it, and good luck.
[Be patient; more material will be added in time, but I’m VERY busy at the moment].