Where to start from?

Firstly, start believing in the fact that UPSC CSE is not impossible to crack. Many have cleared it even without coaching. I myself took coaching classes for my optional subject only as it was a new subject for me (my graduation subject was Physics whereas optional subject was Political Science). There is no truth in the rumor that only brilliant students with 90% above in their career or those who studied in very good colleges get into this prestigious service.

Next, KNOW THE SYLLABUS. Contrary to what many believe not everything under the sun is asked in this examination. There is a limited syllabus for all General studies paper and optional also. Yes, that does cover many things in itself but still you have a ready-made guide available that too by UPSC.

Now comes the important part, what to read and from where?
For this I would suggest to divide the syllabus into following parts for prelims and mains and refer these source(s):

1. Polity- Laxmikant. There is no alternative to this. Use marker while studying and revise as many times as possible. It would be more suitable if you start from Union and State part at the same time. Read President, Vice president followed by Governor. Similar analogy stands true for Prime Minister- Chief Minister, Parliament-Legislative Assembly, Supreme Court-High Court etc. This will help in comparison while studying and it is also a major part of basic understanding the working of Governments in Inida.
2. Economy- Mrunal Patel YouTube channel. Other books like Ramesh Singh is also good but I still believe Mrunal's style is unique and very friendly.
   
   You should finish these two first on a priority basis. Why? Because this is conceptual, helps a lot in newspaper reading and gives you a sense of achievement that you understand things.
   
3.  Geography- Any source is just fine. Be it NCERT (9th-12th) or Majid Hussain or Mrunal's Youtube Channel (I liked the last one). Few things are conceptual, few things you have to ratta mar
4. History- The thing is, you don't have whole history in your course. you just need that of freedom struggle. Read Rajiv Ahir's book on Modern India by Spectrum publication. Also do remember that you have to ratta mar the last pages fully. This is very important for prelims. And read the things that intrest you in art and culture. Questions are generally on difficult side in the second one.
5. Environment- Shankar IAS book is good. Most things are very easy and need only reading. Few things which need ratta  are all the endangered animals and the treaties
6. Current Affairs- Read newspaper daily. The Hindu is most preferred, if not available the Indian express is also fine. But read daily and especially editorial page. Next you can refer Vision IAS monthly current affairs materials which are freely available in their website.

These all are needed for basic knowledge for prelims and form a large part of mains syllabus too. Don't treat the study as different from prelims and mains, remember the knowledge is same, style is different. Nevertheless I will specifically focus on mains practice in later posts.

For those who have time, it is good if you can finish NCERTs. Those who have more than 2 years to appear, Do read NCERTs of 9th-12th. Those who have just 2 years, read 11th and 12th ones. Those who plan to appear just next year, start from newspaper and the sources mentioned above.

Many have asked to shed some light on tests. It is always necessary to give tests for revising and retaining things in prelims. Vision and Insights are pretty decent test makers. But, don't just jump into test series now. You anyways will have ample time if you start 100 days before prelims and then give a test daily. Don't worry about it now.

Please let me know if I should write something more, just drop a comment below. Queries are welcome and constructive criticisms are awaited.