I think the best book on Indian Polity that makes for a very interesting read while exposing you to many important developments in the judicial field is 10 Judgements That Changed India . It covers some of the landmark judgements in the history of our judiciary and in the process expounds many different aspects of our polity. Most of the other books on polity that I have come across are either too technical or deal with some competitive exams. They might not make for a light read.
As for Indian economy the best book I have come across is Economy a Primer for India. The book explains in very simple language the key terms and concepts about economy that you come across while reading a newspaper. It is a very light read and also can be covered in a very short time.
As far as Indian History is concerned, the book I would recommend is the Survey of Indian History by Sardar KM Panikkar. One of the most enjoyable reads in Indian history I have come across. Without using heavy words, KM Panikkar has penned poetry about history. It is a small book but swiftly introduces you to the history of India, the major influential factors during different ages of her history etc. I can vouch for this book. It is a bit old, bit mostly still relevant.
PS: The link to Sardar Panikkars book points to the free ebook available at archive.org. Feel free to immediately start reading.