Which are the best books to start IELTS coaching?

Firstly you need to understand that IELTS is a language-based test that focuses on testing your ability to comprehend, speak and write English. For that, you need to have a basic understanding of the language. If you've spent your entire life studying in English medium schools and reading English books, then it'll be comparatively easy for you to crack the IELTS exam as you've got a taste of this language. 

The listening section involves different accents and complex sentences. Thus, if you have not exposed yourself much to English, then I would recommend you to watch as many English movies, web series as you can. By this way, you can tune yourself to different accents as well as you will be entertained. You could also try taking mock tests available on the internet, especially on YouTube. 

During practice and in the exam, please try to keep your concentration level high because your attention does count. Try to score more marks in the first 20 questions because they will be easy to listen and comprehend.

Coming to the reading section, you need to read a variety of materials viz. articles, editorials of newspapers, stories of different genres. While choosing the article to read, please ensure that the article is at least 1000-1500 words long. I would recommend you to start with the IELTS Cambridge Practice Tests Series. There are 11 books in this series with four full-length Academic practice tests and 2 General practice tests in each book. You could also refer to Barron's book for further information.