How do I start preparations for the civil services exam?

Firstly select the language medium in which you want to start preparations.

Then look for the best and top rated newspaper like Tribune and Hindustan Times.

Setup your Time Table for Study. if you want any reference then you can see on the topic What is the best daily routine for civil service preparation? Here I and many expert share their best routines select what ever you like.

Instead of wasting your time for best books select any Institute that you want to join. I would like to suggest you to go for Crackias an Online Coaching Institute. As they provide you only 10 Red books that has covered all Ncerts from 6th to 12th class (Old Ncerts as well as New Ncerts) and 70 Major sources like Laxmikant, DD Basu, Majid Hussein, GC Leong, Spectrum Modern India, Kashyap, Bipin Chandra, Ramesh Singh, Uma Kapila, TMH relevant portions, NIOS books relevant topics etc. Basically, the idea is that, with these notes, YOU DON'T NEED TO STUDY ANYTHING ELSE For PRELIMS EXAMS.

Then practice more and more for mock test that are also available free from them.

Then go for the old current affairs news beside of the Newspapers. They also provide you the free Current Affairs News Magazines and the topics are subject wise really ease for you all.

Start practicing with Previous Question paper to speed up your paper attempting speed. this is the most important part so that you can attempt each and every Question in the given time.