People sometimes ask me which books I recommend for IELTS preparation and English language study.
In fact, I dont think you need many books at all. If you have some of the official IELTS test books, a good dictionary, and access to the Internet, you have everything you need. Here are links to the only books that I regularly use myself:
For IELTS test practice
I only use the official Cambridge books e.g. Cambridge IELTS book 9.
My favourite dictionary is the Collins Advanced (Learner) Dictionary.
I also use the Oxford Collocations Dictionary for Students of English.