People often ask me about the grammar score in IELTS writing. For example, here's a typical question:
What exactly are examiners looking for in terms of “grammatical range and accuracy”? Are there any specific tenses or types of sentence that should be included in the essay?
Here's my answer:
The main thing is to reduce the number of mistakes that you make. An essay that contains no mistakes is likely to get a 9 for grammar, regardless of the types of sentence that it may or may not contain.
There is nothing in the scoring criteria about including specific tenses or sentence constructions. If there is a nice mix of long and short sentences in your essay, you'll meet the grammar requirements. Remember: as soon as you write a "long" sentence you are naturally going to use connectives (linking words), which will make the sentence 'compound' or 'complex'. So, don't think too much about the grammar - just aim to reduce the number of mistakes that you make, and try to include a few longer sentences.