Booklist for Civil Services Preliminary Exam 2018
First we will go to Polity and Indian Polity by Laxmikant is more than enough to cover Indian polity for preliminary examination. The book has given all the concepts in a very objective and concise manner specially the flow of the book is very nice, so you will be able to read it easily and everything given in point wise manner which make it easy to remember for exam.
For Geography we will prefer Class11th & 12th NCERT and Certificate Physical & Human Geography by G.C. Leong are more than sufficient. However if you are not able to understand concepts from this book you should always refer to Youtube for an animated explanation or some other books available in the market as well.
Ancient History Class XI NCERT by Ram Sharan Sharma, Modern History by Spectrum & Indian Struggle for Independence by Bipin Chandra and for Medieval History Class XI NCERT by Satish Chandra are more than sufficient. We will recommend you for History is that you should always make your notes because History is more of facts that you have to remember and it will be better because when you have compiled your own notes remove the unimportant parts and taking in only the important parts relevant from the exam point of UPSC.
Indian Art & Culture
For this part the book by Nitin Singhania is very good because he has very well compiled the all the part which can be asked in Civil Service Exam. You cam also refer to Spectrum book if required.
Indian Economy by Ramesh Singh is a good book to cover the basic part as well as the parts related to the economic development. Economic Survey is also very essential for this part because many things are directly asked from the economic survey every year. You can also study Sriram's IAS economics notes for some concepts as well as Newspapers / Current Affairs part very carefully because what questions are asking UPSC are generally related to what all is actually going around.
We prefer Shankar's IAS Environment notes because they have very well compiled everything and all the environmental issues which are asked in the UPSC exam then you should also do current affairs this topics. For Science you should refer NCERT but at same time we would say that it is not easy to do NCERT of all 6th to 12th, so if you don't want to go for that you can look for any well compiled material available in the market or online. Do not skip Current Affairs for this section also because questions are generally asked the concepts behind what is happening around.
So, for all above topics the Current Affairs part is very important and we think that these suggested books are more than sufficient and if you are able to cover all these books then you are ready to give preliminary examination 2018. And specially for the people who are giving this exam first time, we would recommend you to get restricted to these resources so that you are able to prepare yourself well. Otherwise those who are giving this exam again we must have covered these books already and they are just doing value addition.