IAS paper I comprises of three main subjects i.e. History, Geography and Indian Society. It is the most conventional among all the four G.S papers and needs basic knowledge of the subjects as questions asked are reasonably predicitable.
Let us discuss the paper subject wise

HISTORY
History consists of four major heads
i) Art and culture of India
ii) World History (including events of 18th, 19th & 20th century.)
iii) Modern Indian History and freedom struggle.
iv) Post independence consolidation and reorganisation within the country.

Art and culture is a very vast topic in itself and these days many questions from this are asked in IAS prelims as well. This topic can be best prepared from NIOS material available online. Some topics an also be found in NCERT’s of class XI and XII (e.g. Chapter 2 & 3 of XII NCERT).

Other reference books could be spectrum’s art and culture and Graphics book on art and culture. It is important to practise the questions of NCERT’s while preparing Art and Culture.
World History covers important events of the c from 18th century. There are three sources from which this topic can be prepared

* Modern World History by Norman Lowe is thesis of 1970’s and most comprehensive book. You can also refer to internet for some specialized topics like the oil crisis of 1970’s and the Gulf War. World History by Arjan Dev and NCERT (old) of class X are also good resources to prepare this topic.

Modern Indian History and freedom struggle is already a well prepared topic by all students even during prelims. NCERT’s are must read for this topic. Besides NCERT’s Bipin Chanra(NBT) and spectrum book can also be referred.

Post Independence consolidation and reorganisation is the most tricky topic of History. Before starting all students are advised to watch all episodes of “Pradhan Mantri” on Youtube.This topic can be prepared from NBT Bipin Chandra-India after Independence( Chapter 6-12) and (Chapter 9- 14) of India after Gandhi.

Indian Society, Women & Globalization
This topic constitutes nearly 20% of Paper I. It can be prepared easily as the questions asked are very general. For Indian Society topic NCERT of Class XII is the best resource to get a basic idea of the topic. Reading editorials from various newspaper can help build on .Inevitably writing practise matters a lot here.

Ref Books
Ram Ahiya’s Indian Society however we suggest you to avoid it. The Role of Women, developmental, urban issues should be prepared form magazines, newspapers and internet. Each year there is a special edition of Yojna magazines covering 1 or 2 topics from this. Yojna, The Hindu and Indian Express are good resources. Students should also keep tab on the website of Ministry of Women & Child Development. For other topics read newspaper regularly.

GEOGRAPHY
Geography portion can be split into three sub topics
i) Salient features of world’s physical geography.
ii) Distribution of Natural resource across the world, industry distribution.
iii) Geographical phenomena.

The first two topics are to be covered from NCERT’s .Old NCERT’s are the best resources for preparing world geography and natural resources. For geographical phenomena G.C.LEONG can be referred. Students are advised to read Geography and You magazine selectively. Candidates should also refer to website of moef and meteorological department of India for updations. The mantra is writing practise. These sources should be read and revised.