This examination requires a wide range of books and study-material to cover the syllabus for each paper at Preliminary as well as Main Examination level.
Instead of picking guides, you should depend on NCERT books (6-12th Standard) for basic understanding and clearing concepts.All these are available in Hindi as well.
Besides, you should depend on standard text-books for all major constituents listed in General Studies syllabus. You can find all most all popular books in Hindi also.
Adopt an integrated approach by spotting common constituents in Preliminary and Main examination and arrange your study material, books and class-notes (if you have joined coaching institute) subject wise and start reading.
Read thoroughly and carefully paying special attention to topics, issues which have been asked in recent years examination.
Cover the syllabus effectively and keep on marking and making notes point-wise to help you in next round to spot important chapters saving a lot of your time.
Being Hindi medium candidate, you need to be extra cautious about Preliminary Examination related requirements and should do a lot of practice to build speed and accuracy.