To get a band 7, you don't need to learn "big" or "difficult" words. You need to learn how to use words together. You need to use good collocations.
Collocations are groups of words that often go together. For example, collocations like "increase significantly" are used in IELTS Writing Task 1.
Look for collocations in the speaking and writing lessons on this website. Here are some examples:
- Health topic: a major cause, poor health, manual jobs, physical activity, outdoor sports.
- Writing Task 1: noticeable feature, significantly higher, a dramatic increase in.
- Describe a person: a major influence, a good role model, inherit traits, set an example, a positive outlook.
Most learner dictionaries now show examples of how words are used in common collocations and phrases. If you read a lot of English, you will see collocations everywhere.